J.T. Realmuto is an elite catcher, clearly the best available in free agency. Forget just free agents, really; he's either the best overall catcher in baseball or close to it. While the Phillies may not have reached the levels of team success they may have hoped for when they traded for him two years ago, he more than held up his end, hitting .273/.333/.492 with 36 homers and winning a Gold Glove in 2019. He made the team better.

In a winter when it's not clear how aggressive teams will be on mid- and lower-tier free agents, Realmuto is still going to get paid, because he's a great player at a position where it's hard to find great players. But he will also be, on March 18, a 30-year-old catcher, and for all we talk about aging in baseball, it seems like there's no position where that takes a larger toll than behind the plate.

So, it's time to look ahead. As we've done with Lorenzo Cain and others in previous winters, let's try to find similar players at similar ages throughout recent history and see how they've aged as time has gone on.

This isn't exactly how teams will view him, but the general idea is the same, and it's going to matter, because this deal could be large. FanGraphs crowd projections, for example, came in at five years and $110 million. That's exactly what ESPN's Kiley McDaniel had. Meanwhile, former GM Jim Bowden, writing for The Athletic, suggested six years and $134 million.

That's a big expenditure. Here's what it could mean.

How have recent long-term free-agent contracts for catchers gone?

We're going to set aside extensions for younger, "face of the franchise" type players like when the Twins gave Joe Mauer eight years and $184 million ahead of his age-27 season and when the Giants retained Buster Posey for eight years and $159 million that begin with his own age-27 season. We're looking for true free-agent contracts, and in the 21st century, there have only been four for at least $50 million for catchers. This just doesn't happen often.

• 2011: Victor Martinez gets 4/$50M from Tigers
• 2014: Brian McCann gets 5/$85M from Yankees
• 2015: Russell Martin gets 5/$82M from Blue Jays
• 2020: Yasmani Grandal gets 4/$73M from White Sox

The first thing that should stand out to you here is that all four were from American League teams, suggesting that they hoped they could use the designated hitter to keep their new catchers fresh and/or transition them there later in the contracts. (This was especially true for Martinez, who caught only 26 games in 2011, missed all of 2012 with a knee injury and essentially never caught again.) We don't know the status of the DH in the NL in 2021, but it's expected to be there long-term, so this shouldn't affect Realmuto too much.

How did those work out? Mostly well. Martin was strong for the first three years, as the Blue Jays made the playoffs twice, and just OK in Year 4 before being traded. That's a good return on their investment. Martinez didn't catch, as we noted, and missed a full season, but when he was available, he always hit, posting a 138 OPS+ in the four years (three seasons) after he signed. Grandal is only a year into his deal, but he was good in 2020 (113 OPS+), along with positive pitch framing. The only lesser outcome here was McCann, and even he wasn't bad, though a 99 OPS+ probably isn't what the Yankees were hoping for.

We'd say the Blue Jays and Tigers wouldn't undo those deals if they had the chance. The Yankees might. There's no reason for regret for the White Sox so far.

That's promising, but it's not exactly what we're after. It's only four contracts, and those four players aren't necessarily similar to Realmuto aside from being catchers anyway. We're not just looking for "free-agent catchers," we're looking for "catchers of similar age and skill." How did those guys age?

So what we'll do is go back in time, look for similar players and see what happened.

How did previous similar catchers age?

OK, first, let's find who those similar catchers are. Let's go back to the start of divisional play in 1969, and look for players who fulfil these requirements over a three-year span.

• Age 27-29
• At least 1,000 plate appearances
• At least 75% of playing time coming as a catcher
• OPS+ between 110 and 125
• Defensive value of average or better

This left us, aside from Realmuto, with 12 other catchers. This makes sense, to an extent, because we're looking for catchers who can hit, which can be hard to find, but not catchers who hit so well that they're far beyond Realmuto's skills (like Mike Piazza). Let's see what happened. Basically, the question is this: You've got to be pretty good to even have had the career to date Realmuto has had. What comes next? Unfortunately, one of the other 11 was Thurman Munson, who died at 32 years old. Let's set him aside, and focus on the other 11.

The good news is, there's mostly good news. As you'd expect, players who are good don't magically stop being good -- mostly -- though there's also some cautionary tales, too. Here's what happened.

Full speed ahead

If Realmuto's next team gets anything like this over the next few years, they'll probably be pleased.

In the late 1970s, Darrell Porter made three consecutive All-Star teams (from age 26-28), and had a 117 OPS+ from 27-29. He never really did end up having a bad season as he aged, as he posted OPS+ marks between 97 and 138 over the remaining six years of his career. He only spent the first half of that span as an everyday catcher, so there's that, but the bat stayed alive.

Bill Freehan was an 11-time All-Star for Detroit, who had posted a 113 OPS+ in his age 27-29 years. He was excellent at 30 (122 OPS+), not so good at 31 (76 OPS+), reportedly while clashing with manager Billy Martin, but he was fantastic at 32 (139 OPS+) and finished off his career with two league-average years. You'd take four good years in five.

Yadier Molina is famously at the center of the "can we quantify everything a catcher does?" argument (the answer, of course, is no), but for a stretch in his late 20s, he had a stronger-than-you-remember bat, too. (He had a 115 OPS+ from 27 through 29.) He backed that up with another great year at age 30 (129 OPS+), and was consistently inconsistent, up and down, over the next five years, leading to a league-average 99 OPS+ from age 31 through 35. Paired with strong defensive value, that's a player you win with.

Mike Lieberthal made the only two All-Star teams of his career at 27 and 28, before missing much of his age-29 season with a knee injury. He was fantastic at 30 and 31 (combined 117 OPS+), and good enough at 32 and 33 (95 OPS+), before finishing out his career with two years as a backup.

Good enough

Rarely spectacular in his long tenure with the Royals, Mike MacFarlane spent the first few years of his 30s mostly alternating good and disappointing years. Bad if you value consistency; good if you average his age 30 through 34 seasons together and get a 95 OPS+. It was fine. Probably not what the team that pays Realmuto will want, but fine.

An eight-time All-Star, Lance Parrish was at his peak as he ended his 20s, and he had a very good age-30 season, too, hitting 22 homers with a 122 OPS+. A good start, but none of the next three years were terribly impressive, before an unexpectedly good age-34 season (123 OPS+).

Ramón Hernández put together three solid years to end his 20s (111 OPS+), which earned him a four-year contract with the Orioles. They were pleased with his age-30 season (111 OPS+), less so with the next two years (88 OPS+), and then traded him to the Reds. He'd spend the next five years kicking around as a backup.

Too soon to say, but good so far

While Grandal is only one year into his Chicago contract, he's two years into his 30s, and there's nothing to complain about here. In addition to his usual excellent pitch framing, he's posted a .373 OBP and .457 slugging in 2019-20, good for a 116 OPS+.

Not good enough

From age 26 through 29, Jonathan Lucroy had a case to make as baseball's best catcher, posting a 120 OPS+ as well as being one of the earliest pitch-framing darlings. His age-30 season was very good as well (123 OPS+), which is valuable, but then ... it was never the same. At 31, he was terrible with Texas (64 OPS+) and good with Colorado (114 OPS+). At 32, he couldn't hit at all for Oakland (72 OPS+). At 33, it was more of the same for the Angels and Cubs (74 OPS+), and this past year, at 34, he got one single plate appearance for Boston. Even the pitch framing suffered.

There was a moment around the turn of the century when the cannon-armed Charles Johnson found life at the plate, as he posted a 113 OPS+ between 27 and 29, boosted largely by a massive .304/.379/.582 age-28 season. He was never near average again, and didn't play after 33.

Finally, Miguel Montero was viewed as one of baseball's better hitting catchers a decade ago, though his age-29 season wasn't actually that good (83 OPS+). He rebounded somewhat at 30 (95 OPS+), but he would never be a regular starter again and played for four teams in his final five years.

***

So, what does this mean? Three years ago, we called Realmuto baseball's "most athletic catcher," focusing on his best-in-baseball running speed and pop time, and noting that he'd been recruited to play quarterback at Division I schools. That maybe underrated him, because he's now more about production than potential, though you might like to think it will help him age well.

The truth is, we don't know. Catcher is a difficult position to play, and all it takes is one poorly placed foul ball to change everything. There's plenty of success stories from similar catchers throughout recent history, however. After all, it's hard to get this good in the first place.