18 - the generally accepted age of majority
It's 16 in Vietnam, Cuba, and Scotland. There's been repeated attempts to lower it in the rest of the UK so 16 year olds can vote.
4 US states, 7 Canadian provinces, and New Zealand have an age of majority of 19 or higher.

The zero escape series sounds exactly like what you're looking for. It's very central to the plot. It's more of a visual novel with puzzles than an RPG though.
Raging Loop is another VN with a similar premise.