I don't think it's an age thing...
I don't think that breeding is as much an age thing as it is a size thing. How long is your female and what does she weigh? How old is she? I think some people try to breed their females at 2 years (after power feeding those entire 2 years) but alot of females are still too small then and it's dangerous. I would say 3 years and a good size (nearly full grown) to be on the safe side. As for the male being too big for her, he won't be if she's big enough to breed.