And yes, the people complaining that games like this are childish are mostly teens.
Exactly, I too am 29 years old. Anyone thinking this game is "kiddy" is insecure about themselves and are too afraid to try something just because of the art design. Trust me, this game is NOT for kids. Any child under the age of 10 would lose interest after the first hour.
27 here. Currently in post-game and have 50+ hours into the game. It can feel a tad childish at times, and the constant hand-holding throughout the ENTIRE game can be a slight turnoff. One last minor gripe is that the AI for your allies is pretty dumb, though nothing game-breaking.
However, that aside, the rest of the game is just brilliant. The art direction of course, together with a good story, plus a pokemon-esque familiar system (and who doesn't love pokemon) leaves plenty to be enjoyed
There's also tons of side/hidden quests, treasures and funny/quirky characters to interact with, and to top it off just sitting down and having a read of the Wizard's Companion just adds to the immersion and 'completeness' of game experience.
This has somewho turned into a mini-review, but I hope this helps you out!