Your girlfriend is much older than you

Usually when there´s a big age difference between daters, one of the partners gets worried that it won´t work. Let´s assume it´s an older woman. Really the issue is her being insecure about being with you.

Usually the older person starts to worry that she´s "not good enough" for the younger person, that the younger person will want to be around people his own age, that the older person won´t keep up, will be too stodgy, that sort of thing. On the other hand, the older person also worries that the younger person isn´t mature enough, won´t want the same things out of life, won´t be content with the (typically) slightly different and slower outlook on life.

There might also be a healthy dose of "what will others think, will they think I´m robbing the cradle" kind of thing. Old-young relationships are ´accepted´ (even promoted) when the male is older, but they´re still frowned upon if the woman is oler.

In general it´s a whole series of her issues that are involved, and she needs to work through them. You can never change your partner ;) So you just need to be supportive, and sit down and ask her (when you´re both comfortable) exactly *what* her concerns are. Maybe even just talking about them will make her realize that some are silly, and any others you can discuss and explain why they´re simply unfounded fears. They´re all in her head, after all, and she should never judge you by your age. She should judge you by what YOU are and what you actually offer, regardless of age.