HoloDust on 30 June 2015
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:
