My sheltie is going to be 1 year old in a couple days and she has drooled since we got her. She drools when she's in the car or waiting for food. I think it's an excited and nervous thing. She would drool with the foamy drool excessively when she was still a puppy but it's gotten better with age but she still does it, just not as bad. It can be annoying when we go somewhere and she's soaked with drool and people want to pet her. I keep paper towels, blankets, and wash clothes in the car when we go places so I can wipe her off. Vet said it's completely normal and hopefully she'll grow out of it.