I have been dating a woman for about 4 months that I have known for 5 years, and she is a little older than me?

I have been dating a woman for about 4 months that I have known for 5 years, and she is a little older than me. We have a great relationship and are alot farther along because of how long we have known each other. We have so much in common and we have lots of fun together. I believe she is the most wonderful person I have ever met, maybe I have the love blinders on but she is more than perfect to me, I adore her. She is everything I could ever want and more, and she seems to be very happy with me(at least I hope so). Anyway from the beginning we knew this would be complicated from the get go because of our age and some other reasons. So she is constantly battling feelings she has that tell her I deserve someone better. That I am somehow missing out by not being with someone my own age. I have tried to explain to her that I know what else is out there and that makes me appreciate her even more. I have been in relationships before and I never realized how happy or wonderful my life could be until I met her. I have no desire to be with anyone else, and she is everything I want, I love that I do not have to compromise on anything because she is so wonderful that there is nothing missing in this relationship. Any advice? What can I say that I am not already saying to make her realize how great she is. She sells herself short in several categories and it is completely unwarranted because she far exceeds my expectations and categories. Please help!