He was fully grown when I got him. So yes, he is both small, and fully grown. Diamond doves are the second smallest dove species in the world, and are native to Australia. I'm not quite sure if he likes veggies or not, but from what I've heard, they'll eat leafy greens if cut up and stringy. I'll have to try it soon.
Here's a link showing the growth of a dove baby from 3 days old, to fledging. Notice how, even on day 21, the chick still doesn't have the adult plumage, nor the orange ring.
http://www.diamonddove.info/bird06_Growth.htmI'm not sure, but I think they get the orange ring when they reach sexual maturity, or at least after their juvenile molt.