How old do pups/dogs have to be to enter this class and what are the other stipulations?

They are for dogs 12 months to 24 months. At my breed shows you aren't allowed to put a puppy in the Yearling Class as they say in the class rules 12 - 24 months only. Not sure if this rule applies to all shows. :)

The dog must be between 12 and 24 calendar months of age on the first day of the show.

If special yearling class 6-24 months