That is pretty small! I kept them a few years ago, and even though had a pair form I never got them to spawn. The male was a complete loco and was too rough with the female all the time. They were probably 6-7" when they decided they are a pair, so urs is definitely quite young. Don't know if they'll spawn for you that young, but since they have their breeding dress on it might happen!
I would be worried a bit if they bred that small. It's a good thing that you have a pair and they will probably bond better if they are so young when paired. However I worry the female has a lot of growing up to do and may use more o her energy producing eggs for the next spawn, than growing up.
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