Birth to 7 weeks: Newborn. There is rapid growth during this time. A newborn can double in size in just a few days. Born with eyes close and hearing not functioning, by the age of 3 weeks, the newborn pup has eyes open, can hear well and is learning to walk.
8 weeks to 1 year: Puppy. The first half of this year, the Yorkie will be a 'young puppy' and the second half of the year from 6 months to 1 year, he will be an 'adolescent'. During this time, a Yorkie is full with energy (sometimes too much), is super curious and habits are being formed. This is the perfect age to train, both for housebreaking and all needed commands.
1 year: Adult. While a Yorkshire Terrier is officially an adult at the 1 year mark, years 1 to 4, he will be a 'young adult'. From years 4 to 8, he will be simply an 'adult'.
8 years old: Most toy breed dogs are declared to be seniors by the age of 8; however there is no official age and a veterinarian may make the 'call' any time from 8 to 10 years old. Most 8 year old Yorkies are still full of spunk and show no signs of old age. However, by the 10-year-old mark, the Yorkshire Terrier is slowing down a bit. He will tire out a bit more, take a new more naps and be much more mellow.