It is true that most dog breeds can live around 12 to 15 years. Depending of course on the living conditions, genetics, and the love received, Shih Tzus can live the same as other dog breeds.
A typical Shih Tzu will live his 13th birthday. When your Shih Tzu is 10 years old, he is a senior. They may suffer from vision loss, hearing, arthritis, and more. We can also say restless sleep, tooth loss, decreased stamina.
The oldest dog that ever lived was an Australian Cattle Dog that lived 29 years from 1910 to 1939. We also have a remarkable record for the oldest Shih Tzu.
It is true that Smokey, from St. Petersburg, Florida made it to the age of 23. It was verified from The Animal Hospital in St. Petersburg that his birth was in 1986. He was in good health all his life.
After Smokey, the oldest living Shih Tzu was Teddy. He died in 2019 and was almost reaching his 20th birthday.