I have had little luck breeding males under 1yr old.

I purchased DJ a male cinnamon in August 2008 he was 150grams. He was the fastest growing ball python I have ever owned he was at least 500 grams and had sperm plugs by the beginning of breeding season. He was continued to grow and eat through out breeding season, he locked up and bred 5 females that year. I produced 0 cinnamons. I backed him up with a more seasoned Spider.

I also tried to use my yearling albino male he was 400g and producing sperm plugs and over 500g by the end of the season. He did not show any interest in breeding at all and was not observed locking up with his het albino female at all that year.

So I would say if your male is large enough and producing plugs go for it but make sure you have a more seasoned male to back him up.