Hi Debby and welcome to BD.org!
Have you given your dragon a name yet?
About the locusts, he should be getting as much as he can eat in 5-10 minutes I believe. He's getting older because he's 6 months. I would give him fresh salad every day to get him used to eating that. When they're adults, bearded dragons eat mostly vegetable matter. About 40% insects and 60% plant matter. Here's a great site that tells you about all the vegetables you can feed him:
http://www.beautifuldragons.503xtreme.com/Nutrition.html. Scroll down a little to find the big chart of veggies.
I would only recommend mealworms as a treat to be used in moderation because of their hard chitin shell and little nutritional value. I'd stick with the locusts as his main staple. You should also be dusting your insects with vitamin supplements. I get Repcal calcium and Repcal multivitamins, the pink and blue containers. On the first link I gave you there is a small chart at the top of the page that tells you how many times a week you should be dusting.
Also, what
UVB light are you using? MVB, tube, coil, or compact? Include the brand and UVB percentage. (example: reptisun 10.0)
What is your basking temperature? (temperature reading right on top of his basking spot)
What is your cool side temperature? (temp reading on the side with no heat lamps)
Anyway, sorry about all the questions and good luck with him!