Here's why:
* The first year of a dog's life is equivalent to about 15 human years.
* Each subsequent year is roughly equivalent to 4-6 human years.
So, a 4-month-old puppy is about 1/3 of the way through its first year, making it around 12-14 "dog years" old.
However, it's important to remember that this is just an estimate. Dog aging is complex and varies by breed and individual dog.