Ha, love the little FFVIII thread breaking out — that's been on my to-play list for ages now. Unfortunately, my to-play list is near as long as my colossal to-read list! Now I really want to play it!
FFX is probably my favourite game ever, back when I played it as a wee 13 year old...
Aaaaanyway, to address the topic at hand: As others have said, it's the way a teenage character reacts and
feels that makes them relatable to readers, not necessarily the actions or roles they're made to fulfil.
A teenager often hasn't had much in way of personal/life experience in all areas of life. Just because they learned to fend for themselves quickly, doesn't mean they also managed to learn all the ins and outs of life, or simultaneously become great lovers etc.
There's a lot more restrictions on them too. Society views them differently, and that has to have an effect on how they behave, even if they've experienced a lot more hardship than usual. A young person will view people of authority differently to an adult, even if they're a rebel with no respect for their superiors.