Prmoise Ring

I have been seriously thinking about getting my girlfriend of a year and a half, a prmoise ring. I feel like we are ready to move on to that next level but my mom doesn`t think so because we are so young. I think that age doesn`t matter, it`s about your feelings for that person. So I was wondering if my mom is right and that I should wait a while longer instead of giving the ring to her in about a month.