The age of consent in Arizona is currently 18 years of age.
Back when this game is set, there's no age of consent because homosexual sex is illegal at the time.
I think you're focusing too much on the wrong thing. It's not been uncommon throughout history for the husband to be 10 or more years older than the wife, and in this time period, noone would bat an eyelid about the age difference... but they certainly would with two dudes boning.
People didn't live that long in 1879 in the USA. The average life expectancy was 39.41. You were expected, really, to already have started having your kids at 18 or younger, not still be 'finding yourself', or waiting a few more years to (legally) start drinking booze... People didn't have the time or money to waste on wasting their lives doing nothing. It was a live hard and die young era. Kids were expected to work, even before their teens sometimes, during this period.
Applying today's standards, laws, and values on a historical time period is not constructive, although, unfortunately, is done far too often nowadays.
Also, there are plenty of real guys who are 18 today who are hot and might be worth throwing a bone, but it doesn't necessarily mean I'm going to marry one... because most 18 year olds are idiots with no life experience.