That's still used as a guideline. But its a guideline. Not a rule set in stone. Everyone decides when their males are ready according to the individual since not all males are the same. As long as the males are in good body condition and are healthy, then why not use them? I personally start breeding males at 500g if they're healthy and in nice condition to endure the breeding season. I don't breed them as much as the older/larger boys. However, sexual maturity plays a part whether or not they actually successfully breed. You'll most likely have greater success with a male that is older than too young.
I've seen breeders have eggs from 250g sires that are 3 months old. I don't really agree with it. I like putting a little more size to them.
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