Yes, it totally depends on age. A baby will eat mostly bugs (crickets or dubias or pheonix worms or silk worms are all great - a mixture of all the above would be ideal).

By the time the beardie is an adult, it should be eating mostly greens. Spring mix from the store is good. Dandilion greens are good. The link above is awesome for figureing out what to try. And just remember, that a variety is important.