that the gecko's size depends on the tank's size?
does it mean that juvenille can stop growing in small size tank?
when should I place young gecko in adult's tank? (30-40 g)?
I dont think they will stop growing due to a small tank, but a baby to juvi can live in a 10 gallon just fine, 20 gallon longs are reccomended for adults, 30-40 gallons are not necessary but it wont hurt anything either.
Actually 10 gallons per adult is more than enough space for leos... That 20 gallon long thing is just what some may rather have over a ten... In my personal experience, all geckos and most snakes do better in smaller housing units...
Cage size will have no impact on growth rate or overall growth... Reptiles never stop growing... They may slow in growth as they mature but they will continue to grow until they die...