No you can not enter in either class. The classes are actually defined as Puppy, 6 & under 9 Months or Puppy, 9 & under 12 Months. So if the puppy is 9 months on the day of the show it must be entered in the 9 & under 12 months. The same thing applies to the 12 & under 18 months class. If the dog turns 18 months on the day of the show it can not be shown in the 12 & under 18 months class. If it turns 12 months on the day of show then it shown in 12 & under 18 months. Should you show in a class that dog is ineligible to be shown in and win, the ribbons will be requested to be returned and any points you were awarded will be revoked.