I believe that if you really think she is the one then you will talk to her parents out of respect for them and see what they tell you and go from there. My bf is 39 and when me and him got together I was 16 and my parents were upset but the more we was together and that the better they got so go for it but be respectful to her parents because she still is their kid and until she is 18 they are responsible for her every action.
Hope it works out for you and good luck.