| I'm sure it's at least 4 months, but I'm sure someone will correct me if I'm wrong. All I've noticed is that my remaining guppy fry must be about 5 months old and she still looks a little small for mating, but I think I'm too protective as she's the only one that never got harrassed to death by the terror fish who has now been separated!
Males however will begin to mate whenever they can, as I noticed with my little Randy (guess how he got his name!?). He was still so small, but trying to mate at any opportunity. His golden moment was sidling up to a molly.
A male molly.
Who swam off in absolute disgust.
Best of luck with it, but the females you get in stores still pop babies out regularly and so far I've not had many probs with fry genetically or anything, they all seem pretty healthy and lively little things with no visual deformities. | 
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