That's the very first time I've ever heard of anyone collecting a stallion as a yearling. I certainly don't agree with even collecting a two year old, let alone a yearling. But they must have felt he was mature enough to test him. It's no different than a yearling colt breeding a yearling filly out in a pasture...they can do it, and the filly can get pregnant; happens all the time. Some are certainly more mature than others.