you can offer these, in moderation, at ANY age. My baby chameleons get appropriately sized superworms from about the second week of age.
Superworms must be gutloaded, and a little calicum dust is usually a good thing too. They have a high fat content, which isnt a huge issue for a young growing animal. Nevertheless, its best to keep superworms to less than 20% of your animals diet. Indeed some would say 10% or less.