Thank you for answering so fast! So, in this case, the justification would be to confine/monitor/support those with unique abilities. That makes sense!

However, I would like to quickly correct you on the canon admission age (sorry!) - my copy of FF8 actually does have it as "5-15" year olds, according to the classroom terminals. Of course, mine is the PAL edition, which has a few small differences (like Selphie's weapon being "shinobu") - I don't know if this is one of them.