Also, I shouldn't have mixed a personal assessment with a generalized assessment. I don't find Gen I to be immature but I find most people like to believe Pokémon is "just for kids" and most of those are people who remember it from Gen I. That's why I claimed it was more immature than Gen I.
Well, I wouldn't say people who say "Pokemon is for kids" aren't people who have played the game, they're the people who have seen the marketing with freaking Pikachu and cuteness everywhere.
Gen VI's handling of the war was with safety gloves. There was no question about morality, it was just a "bad thing". Also, Lysandre was portrayed much more villain than N was (less than Ghestis though...) and lacked proper development.
Lysandre wants to kill everybody because he believes it's the right thing.
Heck, Serena even says "I agree with what Lysandre is trying to say, but his methods are insane!"
That has a question about morality.
On the other hand, Ghetsis wants to take over the world (OF COURSE!).
And, well, if we want to find the "least mature" gen, we should point in the direction of Gen 2 and 3.