@Los Angeles 2021 Parent I actually asked this question this weekend so I can answer as a nosey parent but would also love to hear what others have to say. Out of college, the older player is at a disadvantage in terms of reaching the majors. A 23 year old senior has little leverage in terms of a signing bonus and very little time to prove himself. In theory he is more prepared but statistics show he is less like to reach the majors (see the article I posted below with relevant quotes in italics). Even a 22 junior is at a disadvantage compared to a 21 year old junior. Say he spends a 2-3 seasons in the minors, by the time he's in the majors (if he makes it), he's only got a couple of years before he reaches the statistical peak in his career.
For guys out of HS, extreme youth may be off-putting to some teams because of maturity concerns but the HS guys have a statistical advantage on reaching the majors over college guys. Some if it is because, in theory, the guys who go out of HS are generally top talent. Some of it is related to the statistical peak of a baseball player (just short of 30) and some of it is about the teams looking at players as assets that you either invest in or let go. in their minds, why would you invest in a 28 year old when the next batch is bright-eyed and bushy-tailed and ready to help your team? What I learned was that if you haven't made it to the majors by 26, you will be let go for younger talent that may be equal or slightly less talented than you but has time on his side. Of course there are exceptions. One would be if the team has invested a lot in a player (the more they invested vis-a-vis the signing bonus, the more chances they will give you to succeed) or if you have a special skill or leadership that benefits the team even if you haven't broken through yet. The other factor is none of this matters if you 17, 18 or 19 year old cannot handle the rigors of minor league life...or the physicality of competing against guys 5, 6, 7 or more years older than him.
The most interesting part of the conclusion is once they make the majors, age has no impact on performance!
Here is the baseball-specific article that discusses draft age: https://digitalcommons.macales...ontext=mathcs_honors
Quote from the article: If a player is drafted as an 18 year old out of high school and begins his pro career in rookie ball– which is a fairly regular occurrence–he is likely to be young for his level. If he enjoys success at this level, great, he can be promoted to A ball. Now, take for example the same 18 year old who struggles in rookie ball. Since he is young for his level he may be given an opportunity the next year to try to prove himself worthy by repeating the level–getting a second chance. If another player were 19 years old when drafted and placed in rookie ball and struggled, the team would be less willing to let the player have another opportunity and he may quickly move down the organizational depth chart at his position. Thus, a player who is younger when drafted may be given extra opportunities in the minors, enabling them to reach the majors more often.....
Similarly, we find that given that a player has been drafted, the younger the player is, the more likely he is to reach the majors. But, given that the player has reached the majors, young and old players appear to perform on similar levels.