The actor, now 19, told Details magazine that the age difference between him and his first sexual partner "wasn't ridiculous but it would freak some people out". He chose not to offer any clues about the female's identity.
Radcliffe confirmed that he prefers older women but is currently single because his hectic schedule makes it too difficult for him to have a girlfriend.
The star, who stripped naked for his role in West End play Equus, went on to speak about his plans to continue accepting unusual parts.
He said: "I think part of me would love to play a drag queen, just because it would be an excuse to wear loads of eye make-up."
Radcliffe also insisted that his off-screen behaviour would not shock his fans, explaining: "I don't pretend to do anything particularly wild. People talk about rebellion and they say, 'Where is the teenage angst?'
"But I say I try to do it simply by the choices I make in the work I do. I just like wrong-footing people. I like being different from most of my generation."