I would say it MIGHT be ok but why take the chance. Many illnesses take months to surface, I believe I even read somewhere of someone quarantening for almost a year. Are you sure he doesn't have any parasites or diseases? The only way you could be sure is if you had a fecal done. I would not consider him being alone in a tank at the pet store quarantine AT ALL. Many other animals may carry parasites or diseases that do not effect them but can still transfer to other animals. We have all seen how close reptiles tanks are to each other in pet stores. Also I'd say the most common way of getting parasites is not from other geckos but from contaminated food. If I were you I would wait about three months, however, I cannot give an accurate estimate because I haven't reaserched it enough, I might wait longer.
Also in all honesty leopard geckos do not play. They may appear to interact with each other but they never play. Usually when you see them together they are laying next to each other, this is probably because they have found the most comfortable spot with the best temperature.
Good luck with your leos,
Lisa
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0.1 Hypo Leopard Gecko
0.1 Albino Leopard Gecko
0.1 Blizzard Leopard Gecko
1.0 Albino Pacman Frog
1.0 Lovebird (Tony)
1.0 Elkhound Cross (Otto)
0.1 Malamute Cross (Paris)
6.0 Bettas