I believe they shed from a very young age ( I got my veiled at 3 months old and she was already shedding) for the rest of their lives I believe. When she was growing alot she was shedding about once a month but it seems to have slowed down now that she isn't growing as fast.
Depends on age. When my Veileds were around two months old, it seemed like every two to three weeks. Now it may be once a month or maybe a month and a half.
As they get older they shed less and shed in parts and pieces. They continue to shed until they die, but after about a year you may only have your cham shed every 3-4 months.