You're divorced, I don't see why you shouldn't date. Bear in mind, though, that it's not fair to someone you're dating if you would drop them like a hot potato if your Ex came back.
AS for her age - Age is not the be all and end all, but STAGE OF LIFE is important. It's easy to think "this is just a temporary fling" but feelings do get involved. If she's someone who wants to get married and have her own family in the next few years, and you're someone with no interest in starting a second family - then it would be unfair to date her. If, on the other hand, you would welcome the idea of a second family - then I don't see the age difference as a complete deal breaker. Just so long as the relationship is equal and you're not taking advantage of her, or vice versa.
(I actually dated a couple of delightful young men, they were very compatible on an emotional/intellectual/physical level, but they were at stages of their life where soon they would be looking for a life companion and mother of their children. We stopped before anybody could get too attached, but I could see how emotionally dangerous that situation could be, don't think I'd go there again.)
