I've bred males at around 300g and 6 months old. Whether or not he wants to breed is really up to him, some will and some won't. The only real problem with breeding young males is that they're still growing and don't have a lot of energy reserves, many will also quit feeding while in breeding mode so they'll quit growing as well. They can wear themselves down and be more susceptible to getting sick so don't push them real hard. Keep an eye on their weight and if they start to lose any, quit breeding them and remove them to a different room where they can't smell any females so you can try to get them feeding again. If you don't have a lot of breeding experience it's probably best to wait until next year when he's larger.