How do I break up with a friend?

I am in my late 30's. A lovely person in her mid 20's befriended me. Unfortunately, I just don't have much in common with her. I hate to sound mean. It is a struggle to spend time with her because as much as I try to spend time with her and find something to talk about, it just doesn't flow like it does with my other friends. I have chalked it up to age but I have many friends of all ages. She is sweet and kind so how do I "break up" with her?