My little guy is only 6 weeks old,,,and the breeder that I got him from was already dusting so I continued with dusting,,,so i would say yes,,,begin dusting to help the bones begin to strengthen!!!!
You should only be using the calcium with D3 twice a month. All other feedings should be dusted with calcium WITHOUT D3. Otherwise you could overdose your chameleon on D3. Also a multivitamin twice a month.