Miss Muffet, one thing to remember is that being masculine and being a crossdresser are not mutually exclusive. There are plenty of men who live very traditionally masculine lives and also dress. For some like that, they find crossdressing helps bring a needed a sense of balance in their lives, but the crossdressing does not replace their masculine lives, if that makes sense.
As far as him telling you, don't be upset by that alone. He should have told his ex-wife (she had the right to know before marriage), but this time he did the right thing and told you (because you have a right to know.) It took a lot of courage on his part, and the important thing to remember is that by doing so it means he loves you and trusts you so much that he felt comfortable enough to tell you something he is probably ashamed of, and something that he knows could destroy the relationship. If you can, watch this video from Peggy Rudd, author of "My Husband Wears My Clothes". If you want to understand why your boyfriend dresses, get that book, I can't recommend it highly enough.
This explains how her husband told her, and how he felt about his wife when he told her. It explains what I wrote above about trust better than I could ever explain it.
http://www.youtube.com/watch?v=1pPP6...hannel&list=UL
As a side note, I am in my 30s, and have dated mature women (15-31 years older) so I understand some of the dynamics there. Long down the road you may find issues with the age gap far more significant than the issue of his occasional private dressing; I don't say that in any way to dissuade you from being with a more mature person, but there are issues involved there that, like the crossdressing, need to be discussed before you make any commitments (especially any irrevocable commitments) in the future.