Are you asking which will finish on grass? Or which can graze and produce calves. There's a major difference. If you're asking about grass finishing, at what age do you want to finish? There are several breeds who are known to grass finish by 18 months of age. These include but are not limited to Murray Grey, Piedmontese and some Angus, some Hereford. If you get too large a frame on the animal, they grow first then finish. Thus Simmental, Charolais etc can grass finish but they'll be a lot closer to 2+ years. Look for marbling, (this can be a problem with Pieds) easy doing and smaller framed deep bodied cattle. I'm certain there are sites which would give you much more information.
If it's cows to graze and produce calves, every breed can work, but not everywhere! Some cattle require more nutrition than is available in some areas, say a simmental in Arizona on native pasture (if there is such a thing) would likely not do very well.
