Over the past few years, Major League Baseball has been trending younger, with the average age of Opening Day rosters dipping below 29 years old for three years in a row, including this season.

Since this season has started, teams have been getting even younger. A large number of prospects have been getting big league time this year, including many elite-level players. From White Sox outfielder Luis Robert, who was on an Opening Day roster, to the most recent Top 100 callups, like the Giants’ Joey Bart and Sixto Sanchez and Jesus Sanchez of the Marlins.

Just how unprecedented is this? Take a look at the number of team Top 30 prospects and Top 100 prospects in the big leagues as of August 20 over the past several seasons:

2017: 32 (10)
2018: 29 (3)
2019: 36 (5)
2020: 79 (23)

That's more than four times as many Top 100 prospects and more than twice as many Top 30 guys as there were a year ago. And that Top 100 total doesn’t even include players who were once on a Top 100 list: Isaac Paredes (Tigers No. 6 prospect), James Kaprielian (A's No. 13), Luis Garcia (Nats No. 2), Jorge Mateo (Padres No. 15), Monte Harrison (Marlins No. 10), Justin Dunn (Mariners No. 8) and Triston McKenzie (Indians No. 9).

This is so statistically significant that it’s worth digging into further. In talking to general managers, there appear to be a number of factors, and not all are due to the unusual parameters of the season. For some teams, like the Mariners, the number of prospects who have gotten big league time in Seattle likely would have happened in a normal 2020.

“For our part, we’re in the midst of a rebuild and have the youngest roster in baseball,” Mariners GM Jerry Dipoto said. “Our goal was -- and remains -- to develop a sustainable core and we believe we’re on the right path.”

It really started last year with Seattle, as young players like J.P. Crawford, Kyle Lewis, Justus Sheffield, Shed Long and Dunn, established themselves or at least got their feet wet. Evan White was added this year while Top 30 prospects like Braden Bishop, Taylor Guilbeau and Ljay Newsome are getting chances to show what they can do.

“Last year, mid-to-late season we began introducing the first wave,” Dipoto said. “This year we added another, while also committing to providing opportunity for this group to gain experience. I would anticipate the next wave beginning to arrive at similar junctures as we move toward and throughout 2021.”

While there are other rebuilding teams, like the Tigers, who called up top pitching prospects Casey Mize and Tarik Skubal this week, this youth movement is not limited to those looking to next year and beyond. The A’s are in first place in the AL West and are relying on Top 100 prospects Jesus Luzardo and Sean Murphy, while also recently calling up Kaprielian to help. The White Sox are competing with Robert in the lineup and Nick Madrigal getting a chance before getting hurt, while also recently calling up Dane Dunning to help the pitching staff. The Marlins are at .500 right now, to the surprise of many, while not straying from leaning on their vastly improved farm system.

Even for teams like the Mariners and Tigers, how this season has played out certainly has made it easier to call up more prospects. There seem to be three main factors:

1. Rosters are bigger. The season began with 30-man rosters, which were then cut down to 28. The initial plan was to trim down to 26, but that’s been scrapped. Extra spots mean extra opportunities.

2. Injuries. There have been a lot of them, and some have been season-ending. As a result, prospects who were in 60-man pools and in alternate camp have been called upon to fill in the holes.

3. Lack of other development opportunities. Yes, players are working out at alternate sites. And they are having simulated games of some sort. But it’s not the same thing as playing every day at the upper level of the Minors. And there aren’t enough players at the alternate sites to play full games, with some games ending with, say, no left fielder or a pitching machine on the mound.

That makes it easier for teams to decide to fill those extra spots with prospects. In past years, there would be hesitation to bring up a prospect, especially a top one, if he wasn’t going to get regular playing time. While teams have tried to make alternate site camps as constructive and beneficial as possible, there don’t appear to be the same concerns about removing young players from developmental routines.

Here are the 23 Top 100 prospects currently in the big leagues:

3. Luis Robert, OF, White Sox
4. Jo Adell, OF, Angels
5. Casey Mize, RHP, Tigers
6. Jesús Luzardo, LHP, A's
7. Cristian Pache, OF, Braves
8. Joey Bart, C, Giants
9. Dylan Carlson, OF, Cardinals
10. Carter Kieboom, SS/2B, Nats
11. Sixto Sanchez, RHP, Marlins
12. Luis Patiño, RHP, Padres
13. Brendan Rodgers, 2B/SS, Rockies
14. Alec Bohm, 3B/1B, Phillies
15. Sean Murphy, C, A's
16. Spencer Howard, RHP, Phillies
17. Tarik Skubal, LHP, Tigers
18. Nico Hoerner, SS/2B/OF, Cus
19. Evan White, 1B, Mariners
20. Brady Singer, RHP, Royals
21. Keibert Ruiz, C, Dodgers
22. Daulton Varsho, C, D-backs
23. Jesús Sanchez, OF, Marlins
24. Brusdar Graterol, RHP, Dodgers
25. Andrés Giménez, SS, Mets
    Complete list »