You could probably be feeding a bit more live insects at his age, although at 20 inches he's pretty close to full grown I'd imagine.
I'd key him have a big salad every day and up his feeders a bit. The Phoenix worms are really small for a 20 inch dragon. I'd up the number of Phoenix worms.
Other nice feeders you could try to add for variety sake would be silkworms, hornworms, dubia roaches, butterworms, and crickets.
He doesn't need much more imo since he's so big already. I'd focus on keeping a salad available to him all day.
-Brandon