I meant to weigh in on this a couple weeks ago but never got around to it. We take all our bull calves to slaughter within the first year, anywhere from 6 to 10 months of age, while they still qualify as "veal" (
Rose veal, in our case). We do this for a few reasons: we're able to get the calves off the farm sooner, for better cash flow; it gives us a unique marketing advantage in an area dominated by beef; it allows us to keep more mama cows, since we don't have pasture tied up by fattening beef steers; and it makes something tasty and worth eating.
Compared to beef, Rose veal is leaner (you may or may not consider that a good thing), milder in flavor, sweeter, and considerably more tender. If you want a really nice stock, you'd be hard pressed to do better than one made with veal bones.
The distinction between "veal," "baby beef," and "beef" is not clear. For our purposes, it's only "veal" if the USDA inspector declares it so. Technically, I think, anything under one year old is "veal," but it all comes down to whether or not the inspector declares it to be under one year old. (This is not an exact science.) I believe "baby beef" is just a marketing term and isn't recognized by the USDA. None of that matters when you're producing for your own table, of
course.
Another thing to consider is the cost of gain. I have no figures at hand, but a smaller animal is going to gain weight more quickly and more cheaply than a larger animal, because less of its food has to go to body maintenance. This is why, on the commodity market, the price per pound (live weight) decreases as weight increases. "Cost," in this case, doesn't have to be merely financial. You may find that, for a given poundage of forage available, you can produce more "veal" meat than "beef" meat, making the younger animals more economical, though that may be offset by a higher processing cost per pound.
Anyway, all that said, there's no particular reason, in my opinion, why you ought not slaughter a bovine at one year of age or less. (Technically, for what it's worth, a "yearling" is anything one to two years old. If you're slaughtering this year's calf, it isn't yet a yearling.)