Not the original poster, but I think the point is that kids with an age advantage get ahead early in sports and never look back. For example a youth hockey player with a January birthday, which makes him the oldest in his age group, is likely be better than a kid born in the later half of the year during the early or mid years of his youth career when he is learning the game. Once the player gets to HS or college, the studies show that the January hockey players are statistically better than kids with later birthdays, even though 6-9 months difference should not make a difference at that point. So for lacrosse, if a family wants to set up their son for success in HS and college lacrosse, holding back gives an advantage. If one team has a higher concentration of hold-backs than others, it gives that team an advantage.
Ultimately the advantage goes to the one that is better academically. All of the top D1 programs are also highly selective schools. A lot of kids are good at lacrosse and so it comes down to academics. Coaches are going to pick kids that can do well in the classroom. If you can't be academically on par with the average incoming freshmen you are not going to that school.