Here is a good food chart that color codes the best feeders and vegetables. At 17 inches your dragon is big enough to have the occasional superworm as a treat.
http://www.beautifuldragons.com/Nutrition.html
I start feeding my dragons live feeders only once a day around 5 months but they have access to salads and veggies all day.
Body condition will also play a role in when a dragon is switched to the adult diet, not just age. Daisy was switched to an adult diet around 10 months, per vet instructions.
DaisyDragon from Carolina Designer Dragons
The above picture is Daisy at 10 months when the vet told me to switch her to the adult diet, which is 80% plant/veggies and 20% protein feeders with very limited fruit occasionally. She gets salad with veggies every day and one or two crickets (or other suitable feeder) every other day. She basically gets about 7 crickets a week.