Yep, rpg's is more of a teenage genre. Although more adults are playing video games all the time most adults play games like World of Warcraft, shooters, or sports games. Very few delve into the lands of console rpg's.
The people who make video games know this so they try to create worlds and characters that those 12-17 year olds can relate to.
In movies a very young character going on adventures like this often tends to be no younger than mid to late twenties and the main characters often tend to be in their thirties and forties. However to a fifteen year old someone in their thirties or forties is considered old so they don't relate to them very well. The fifteen year old can relate to other teenagers much better and young to them is like 8 or 9 (which not coincidentally often tends to be the ages of the youngest characters in the group of many rpg's).