I have sold mine at two months, so far I have only sold them to reptile dealers, I think if I were to sell them to an individual I would wait a little longer. But generally speaking they are strong and healthy at that age. If some take a little bit longer to mature then wait to sell them. I also think that it is important to keep a detailed record of your hatchlings and keep track of when they were born.
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2.2.5 Crested Geckos
2 ringneck snakes
0.1 packman frog
1.1.1 Box Turtles
1 Redclaw Scorpion