As the dragon is already a year and half old, he should only be fed crickets two or three times a week, offered mixed greens (collard greens, mustard greens, Escaroli, dandelions, Enchive as stables daily. Romaine, parsley, alfalfa sprouts, mixed frozen vegetables (thawed and bigger pieces chopped), zuccine, bell peppers can be added as garnish and variety. Fruit and flowers can be offered as treats as well, such as strawberries, grapes, melons bananas (rarely!), hisbiscus flowers, dandelion flowers, there are a few others but can't think of them right now). Greens should be offered daily every day. As the heat lamps tend to dry out the greens fairly quickly, either mist them regularly throughout the day or replace in the early evening (5pm or so).
Crickets are good to feed them, dust them once a week with a calcium suppliment and multi vitamin. (repcal with D3, reptimines). Mealworms and superworms can be given as a treat or to use for training but not to excess. Waxworms and pinkies both have alot of fat content and should be used as mentioned before, to females after laying eggs or to beardies recovering from illness. Silkworms can be fed instead of crickets though they tend to cost more. To offset cost, they are bigger and more filling (not to mention quiet, easy to care for, easy to clean and odourless..well except for a leafy smell from their poo).
Other than food, ensure he has the proper lighting. A good UVB tube/bulb (Reptisun 5 or 8, Powersun Mercury vapour bulb, also doubles as heat) and a basking light which provides a basking site temperature of 95-105 F. Make sure there is a cool section in the cage (which by the way should be at least! 4' long by 2' wide by 2' high. Larger is always better) that is about 80F during the day. Nightime temperature should be around 75F.
Hope this covers all the basics. Oh use either paper towel or washed play sand for substrate.