India, Turkey, and most of eastern Africa are the majority of the places that match the 10 US states that set it at 18. (7 US states set it at 17.)
However, since most of our movies and media are based in CA and NY, and they are both set at 18, the popular notion is that 18 is the age for most or all of the US, but it isn't actually so.
Mexico (many provinces at 12, 13 or even puberty), Argentina and Niger (13), and Angola and the Philippines (12) are at the opposite end of the spectrum.
Indonesia is at the top at 19, and most of the Muslim world demands it only after marriage, but since marriage to 9 year olds is permitted, it's hard to say that they are the most conservative.
Ireland (at 17) is apparently the only place in Europe over 16.