We started ours at a week. Now at two weeks we have them in the yard for an hour or so and they LOVE LOVE LOVE ants. If you want some fun, go buy some small crickets and let them loose in the brooder.
They love crickets, but will eat most any insect small enough for them to eat. Those little round sow bugs (My kids call them rolly-pollies) mine seldom eat, but anything else they can catch they enjoy. Crickets, grasshoppers, moths, flies, just any small insect they can catch!