I think in AKC they have to be 7 yrs old. In CKC they have a pee wee class where it's even younger, 4 yrs. And in UKC they can be 2! lol And I think in the youngest ones they can have an "assistant" handler. 🙂 I know I've seen Laurie Soutar going around the ring with her granddaughter in UKC. She has Lakilanni Greyhounds and are regulars at the lure trials.
PS, that's for juniors. I think for the breed ring there is no age stipulation as long as they are in control of the dog. Kathy?