I don't believe yearling bucks collectively should NORMALLY shed before 2 1/2 and older bucks. But I do often see particular yearling bucks that have no antlers before I see most bucks without antlers, keeping in mind every individual buck (regardless of age) has his own "normal" shedding time throughout his life, i.e. some individuals normally shed earlier than most, year after year.
I think it may be more common for yearling bucks (than older bucks) to lightly but traumatically knock off their antlers immediatly prior to natural shedding. I've noticed several early shedding yearlings to have pedical damage, such as maybe there was some light sparring, or possibly just touching the ground, etc., causing the loosening antlers to break off (at the base) prematurely. My thinking is the yearlings are just less experienced at protecting their headgear, and having smaller bases, they would likely "break" off easier by accident a few weeks before simply falling off more "naturally".
The above not to be confused with older bucks "breaking" their antlers while fighting, etc., where "breaking" antlers around the rut may be more common with older bucks.