Wow, funny you should ask. I am 23 and my fiancee is 45.. er, 46 in a couple days... (I also have a bday yet this year, so we are 22 yrs apart). For us, it was a match made in heaven. But age does not really have anything to do with it... it's all about personal experience, life expectations, and shared interests. There's not many guys my age who enjoy swinging, but my fiancee does... we also shared careers and many other interests. But that does not mean everyone in this situation does. Heck, people exactly the same age do not necessarily share the same interests and hopes/dreams/wishes for their lives...
If you don't love her, you cannot force yourself to love. It hurts to break up, but if there is no future, then why draw out the inevitable?