Hello, James!
I agree with Allin on most points.
the fact that she is older might be intimidating to her. and the fact that it's your first relationship with a woman may make her think that your feeling for her are .... temporary ...
anyway. i was in a similar situation when i met my first love.
i had had 2-3 boyfriend before i met him. and i was so disappointed in guys - didn't want to date anyone ( and i didn't for 2 years). but with Him i felt sooo comfortable, so right, and so myself. i didn't feel that i needed to impress him ( and he liked me just the way i was). and i remember that I wanted to stay friends with him forever (just because being friends can be really a long term relationship, unlike being in a romantic relationship).
We would hug and hold hands, and sleep on the coach hugging each other.
i think those were the best times ever)).
but, he wanted more and i was not ready. he was pretty patient)) and i am glad he was. a few months later, i caught up with his feelings and was able to reciprocate
i think this girl must have had terrible experiences with previous boyfriends (my experiences weren't that terrible, but still i did't want to date for 2 years!), and so maybe she does not want to lose what you two share right now - special and intimate friendship.
what i would do if i were you, is ask her, why does she think she can never love you. that's what bothers me in this story((. she acts like person who is in love, said that she would marry you, but at the same time she is convinced that she does not and will not love you.((
talk to hear about it. It's probably something that's hard to reveal (for her), but you will know what to do going from there.