Little Inferno is an addicting game that is geared towards older kids. It has great physics and is fun to play with, and it's fairly addicting.
It can be mildly disturbing, and it has a couple things related to drugs and alcohol such as "Mommy Meds" and midlife crisis wine, but they're in there for humor. They're by no means advocating anything.
It does have some environmental and anti-consumerism themes, but overall, the main message is, "Don't waste your life and time. Get out, meet people, explore. Use the time you have wisely. Make your life worthwhile."
As for age, I'd recommend it for ages 12-13 and up.
In short, it is an excellent indie game with a deep meaning, and is, in my opinion, worth every penny.