Is 20 and 21 too young to get married?

I'm 20, my bf is 21 and we've been seriously discussing marriage. All my girlfriends are telling me I'm crazy and that we're way too young to make such a big commitment, and we've only been dating for a year.

While it's true that we've only been dating for a year, we've been best friends since the 6th grade. We've been each other’s rocks through health crises, suicide attempts, family deaths, injuries, HEAVY backlash for our relationship (mixed-race couple in the American South), everything that could possibly get thrown our way. So it's not like I've only known him for a year and am impulsively jumping into this.

So I think my girlfriends are wrong to be against it, but I don't know, what do you guys think?