I would love if with what ever character they choose, if they choose to have an Aqualad, that he really is a teen and not over 21 or something. If you do a version of say Kaldur, make him a legit teen. The argument against the teen sidekicks in live action has to my mind only ever really applied to two in the DCU: Speedy and Robin. And with them you still can fudge a bit if you really put a focus on their fighting ability I think. The hurdle of the audience buying these young characters operating alongside seasoned super heroes has a great leveler in the context of super powers. Is it ridiculous in a "realistic" sense for Superman to take a 15-16 year old girl into a dangerous situation? Yeah. But make that teenager his super powered cousin and it's easier by far to adjust to the idea. Most of the traditional teen sidekicks of the DC heroes are super powered, and this includes any version of Aqualad.
Having Aqualad as a teen if executed well, would add real pathos and weight to a dilemma of having "two fathers/mentors" in my eyes.