They could be too large, but he may just be tired of them. The crickets should be no wider than the space between the beardies eyes. If they are wider than that, they are too large.
If he is tired of them, consider another feeder like silkworms, phoenix worms, roaches etc... Whatever you do, please do not feed anymore mealworms. Mealworms have a high chitin:meat ratio (meaning they have a lot of undigestible exoskeleton to the meat) and this carries with it a high risk of impaction, which is not good at all. They also are not very nutritional and should just not be fed.