Can an illegal mexican get gay married?

ok so im 16 and i have a girlfriend, shes 16 too and we've been together for a long time now and i feel like i wanna spend the rest of my life with her but shes illegal!! i know we need to be 18 to get married but iwanna surprise her with the idea for our next anniversary and i need to know if we can get married when we turn 18 and if we can, what do we need (important papers) ???