The Justice League were discussing the age limits for members as the team's younger successors and sidekicks all talked and trained. Practically the entire Young Justice and Teen Titans team was there along with a few extra vigilantes and heroes.

"Do can we agree that 18 is a suitable age for joining?" Superman says

"Well what about Superboy(Conner), he is less than a year old but has the maturity of a young adult. Should he have to wait 17 more years?" Wonder Woman points out

"So will the dividing factor be between biology or maturity?" Martian Manhunter asks

The younger heroes were also questioning the rule and as you and Robin(Damien) spar you point out a small factor to your own age.