Technically PA is 8 weeks for dogs and cats, no real mention of rabbits buts thats the guidelines that I follow. Since I make the first cut(whose staying whose going) at 8 weeks it does work for me, and most Pet Shops follow the 8 weeks guideline. Which is what it really is with rabbits in PA, I used to think it was the law until I took the time to read the language, which doesn't really include rabbits, or cavies or any rodents. Or chickens for that matter, which by the way the USDA considers rabbits 'Poultry'. Haven't figured that one out yet. There are ways of telling their age, body appearance of course, but the biggest one is coat, particularly with a chinchilla colored rabbit. They start to change out of their baby coat, and you can tell by the emergence of the new coat roughly how old they are. Works well with fryers, and older juniors. If all they have is baby coat and a baby looking body you can hazard a guess on age as well. White is harder to do this with. I've sold rabbits as young as 6 weeks or so, PA used to be 7 weeks until the law changed 3 years ago. I don't do younger because I have a good working relationship with the places I sell to, and dead bunnies is bad for business. Better to hold them a bit and make certain their ready to go.
But what about selling to 4H kids for meat pens? Many 4H kids buy their meat pens at a young age and then raise them for the fair, wonder how these laws would influence that situation. Think their supposed to have the kits by 4-5 weeks and raise them to 10 weeks for competition. I'll have to check into that.