I have never had a relationship with an older woman but I am definately interested in it. I think what appeals to me is a sense of identity, accomplishment, security (in herself, mentally, physically, etc.) that younger girls just simply do not have. When it comes to the more 'serious things' (i.e. when we're not just goofing around and enjoying life), I tend to be very mature for my age. This probably fits in somewhere too, because all of the girls that I am around (except one or two I can think of) at college are very immature and usually seem to suffer from some kind of identity crisis, which is somewhat normal considering the age and all the experiences/changes etc., people go through.
Aside from those mental aspects, which are really attractive to me, I also find a woman who is out of her 20's, but still maintaining her beautiful body to be extremely sexy. I think this comes down to actually proving that she takes care of herself (and if she can take care of her own body so well.. perhaps it leads me to think she can take care of other responsibilities in her life also?). Just about all women look spectacular at age 20, but as some others on this post have said "let themselves go" at some point. I like to take care of myself (i.e. keep clean, eat relatively well, but not as far as super-nutritionist/exerciser/bodybuilder at all, just a general good up-keeping) and I think it is attractive to find someone else who does the same.
So, I wouldn't be surprised if I end up with an older woman at some point in my life. I don't specifically target women based on age group though, since I still like women my age also. I guess I'd say that I don't descriminate based on age at all, so that leaves many possibilities open.