Veiled chameleons tend to eat greenery from the start. The environment they come from is harsh and insects are plentiful at some times and sparse at others. They have to eat whatever comes their way, including plants. They will eat insects first, then if they are still hungry, go after plant matter. In captivity, they might go after greenery first if they need a certain vitamin or if they need water. Feed a combination of greens, vegetables, and fruits with a combination of vitamins and minerals in them and they will get some of their supplementation from that.
My veiled started in on the pothos when I first bought her at about 4 inches long. She must have been at least two months old at that time. I am uncertain of her age as the store did not specify her age.