Well mine grow wee things early on, and I have the odd one that goes abit further (and then usually needs trimmed as it grows in an odd angle, like straight into the eye...), but almost all knock theirs off while still lambs and have a small bare patch of skin. My ewes are polled, but the interesting thing was that the Bowmont Shetland X boys had quite strong wee stumps on their head - as they also have a topknot of long wool, well hidden, and numerous bruises on my legs later....
So with crosses horns are a bit of a lottery!