6 Things Final Fantasy Can Take From Suikoden

[Randy]

Well yes, they obviously twist reality a bit to contrive a cast similarly aged as their audience. If they didn't do that, they'd have to just ditch their majority age demographic or just set every game in a school or university (FF8 garden for example, desperately failed to not be a school)

As for the variety of ages for different attributes logic, well the problem is that leads to massively overused stereotypes. So you get the wise old man, the naive and energetic young girl, the big muscular but dumb man.
That's very often the outcome when you construct a cast "backwards" (if you like) i.e you decide roughly the range of attributes you want first and then create the cast to that specification. The alternative which leads to more realistic storytelling is just inventing the characters first and then trying to reason through how this cast would deal with the situation you give them. With that way of thinking, it often pays to change up the formula from time to time to get different results. Which is why I like the idea they're going with 4 guys of the same age for FF15. Not many JRPGs have done that.

As they pointed out in an interview, you can do things with that cast, like having them all sleeping in a very small tent out in the wilderness, that you couldn't really do with other casts (you certainly couldn't do it if there were a few romances going on between the people in that tent)