I'm not a fan of the age limits in general. We are allowed to carry over 200 minor leaguers. If a GM wanted to "horde" any class of prospects, they have the ability to, regardless. I think it adds extra work without doing anything positive for the league. Just my two cents.
There are limits in the minor league systems for Minor League Service Time. This is harder to track for me and I think this is why originally there was an "age limit" added. Before my time though.
Here is the typical breakdown.
AAA - no service time limit (therefore no age limit)
AA - no service time limit (therefore no age limit)
Adv A - max 2 players with 6+ years of minor league service time (we have no age limit)
A ball - max 2 players with 5+ years of minor league service time (2 over age limit 26) - we could change this
SS A - max 3 players with 4+ years of minor league service time (4 over age limit 22) - can adjust
AZL or Rookie Ball - no players allowed with 3+ years of minor league service time (15 over age limit 19) - can adjust
DSL or VSL - international players only and no players with 4+ years of DSL/VSL service time (15 over age limit 19) - can adjust
Now these are the things I do know, I am not tracking minor league service time. LOL. But I would feel fine adjusting the age limit to 22 for the 3 bottom rookie teams instead of 19. Guy gets drafted at 18 out of high school and plays 3 years gives 3 years to 21.