I'm not 100% sure (I don't know if anyone is), but I think Convicts are sexually mature at 5-7 months of age.
And by 'rebreed' do you mean breed the fry to the parents, or fry to fry? In that case, yes. It's fine, it's called linebreeding, and is a very useful method of "locking in" a desired trait in your fish.
And by 'rebreed' do you mean breed the fry to the parents, or fry to fry? In that case, yes. It's fine, it's called linebreeding, and is a very useful method of "locking in" a desired trait in your fish.