Seriously though there is a reason most JRPGs dont feature characters over say 25 and its because of there target audience which is mostly going to be Japanese teenage males.
Anyway you can tell me its more realistic that a guy like Nagi is going to save the world compared to say Noctis but wholly shit do I already hate Nagi.

Bingo. Japan does this all the time. All those loli girls with obvious 12-14 year old anatomy but given an age of 18. Age rarely has any relevance in Japanese games. 

Same With Romancing SaGa 3. 25 plus with very characters under 

Any JRPG with a lot of military influence will have a wider range of character ages. That's pretty easy.

why not ? he already more awesome than entire ff xv cast 

and they'll probably behave like teenagers.

Yea, the usual RPG cast is always highschool teenagers for some weird reason.

did you played that game already?

the only character behave like teenagers are lin well because she is 13 , want me to spoiled you about characters story ?

elma is opposite of lightning = cool and not emo(crybaby) , self dependant , didn't blame others for their mistake and always giving advice to younger soldier 

doug = big man but with soft heart . ace pilot and expert on military combat , lao = he *spoiler* yes pretty dark background 

there's only 2 character with teenage attitude that is lin and ruu native mira inhabitant 

please this is not star ocean franchise where all people act like teenagers

Sup Zero or clone of Zero. What I've bolded is exactly how Lightning is. I unbolded cool because it's subjective. I think she's cool.

For some reason, I see this thread as connected to recent JRPG thread about why western gamers don't like it, so I'll approach it from that angle.

I don't think it's the age of characters per se that is the problem, it's how are they designed.

For example I can completely believe that Bjorn from Vikings is warrior in his teens, or that Miyamoto Musashi had his first duel in 13. But most of JRPGs cast characters that are very young and that look like they would be better off singing in boy/girl bands instead of fighting.

Those pics can really claim any random number of years, but (except for Doug and Nagi) I would believe them when I see character design like this: