It's never too early to introduce new foods to his diet. Both worms are excellent feeders, and he'll probably love both of them.
I've never had a chameleon go on any sort of strike, I think because I offer a lot of variety all the time. So crickets are the staple but they aren't 90% of the diet, so there are weeks where they may not see crickets at all and others where they will see them a lot more often, but I add in horn (goliath) worms, silkworms, butterworms, grasshoppers, supperworms, 3 types of roaches, and whatever I find outside that's safe to feed off. They get an average of 3-4 different insects a week.
Mixing it up for him will keep all food items more interesting, I think. And if he does get tired of one then don't use it for a little bit and reintroduce it after a few days. Feeder variety is also good for stimulating them mentally, it keeps things interesting for them.
