Just how old does a gold fish have to be before it can breed? Or how young can it be ?

Unfortunately, size doesn't say anything about age a lot of times. You can have a monster fish with 8 months old, or a tiny little stunted one with 4 years of age. But in general, fish are in their prime years at 2-3 years of age, and generally somewhere above roughly 3 inches. How old you think are your fish right now?

Oh Gian is 3 that's a positive, but my daughter wants these two little tiny commons they can't be more than 4 or 5 months I think, they are about 1 inches each, and I am not equiped for babies currently. And I thats why I was wondering how old before they start maturing enough to reproduce.

My fry at 5 months of age developed his breeding stars and started chasing the ladies. I am not sure how fertile he is though.