There is no "too young" when it comes to aggressiveness. Sometimes my 5 mm fry would flare but there is no real aggression at that time. Some of them may develop aggressiveness very young while others may wait till an older age. This is why show fry are jarred since the age of 2 months (about 8-9weeks).
If perfection is important, then you should isolate/jar the aggressive ones. Otherwise you could keep them together a bit longer and see if the aggression dies out. If often disturbed (like moved during water change) or if they are stressed in some way, they will become aggressive sooner. But if undisturbed, I could keep mine docile until 4-5 months.
If perfection is important, then you should isolate/jar the aggressive ones. Otherwise you could keep them together a bit longer and see if the aggression dies out. If often disturbed (like moved during water change) or if they are stressed in some way, they will become aggressive sooner. But if undisturbed, I could keep mine docile until 4-5 months.
