Depends on the circumstances. If someone were legitimately curious about being transgender, it may be I would be the only trans person who would be willing to educate them first hand (which is the best way to be educated). Or if it was someone I was becoming friends with, I wouldn't hide that part of my past from them (and face it, most of my past was as a male).
If someone just wanted to see whether their guess and my gender history was correct, I would try to avoid giving them the satisfaction.