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.
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.