Depending how much it grows it will shed when it needs to. Sometimes it might be every month to two months, every month is usual for a younger one, and it takes a while longer for the adults. In my experience anyway.
Don't worry yourself too much if he/she doesn't shed when you want him/her to. It just depends on how much he/she grows and how high the humidity level is. Keep them while misted and humid when they are shedding it will go quicker that way.