I think 18 is reasonable . Legal adult age .
If you can make a choice to be a father, jailed as an adult , ride a Abrams tank , be a race car driver, Be a policeman , then why not try and make an NBA basketball team.....surely their are worse things you can do .
Any limit over 18 is a selfish and unfair restriction to assist in an agenda that doesn't really have the best interest of the individual as the prime objective.