When it comes to an age to marry there isnt one. Its all about love and maturity. Each individual knows when they are done with the dating aspect.

Im sure she does love you. If you cant love her then the longer you string her along the more strings she will have to get caught up in. I believe that you care about her and are not mature in life to take the next step. You should tell her exactly how you feel. Its not that you have done anything wrong. You took the first step by aasking for help on this. Now the rest is for you to find in your heart. Good luck