How old is a 9-month-old puppy in human years?

≈ 11 human years.

Height is close to final for most breeds, but the chest and muscle keep filling out.

Breed size hardly matters yet. A dog's first two years run on the same fast schedule whatever the breed — the first year is worth about 15 human years, the second about nine more. Only after age two do small and giant breeds start to diverge, and then quickly.

Nearby ages

6 months8 human years
7 months9 human years
8 months10 human years
9 months11 human years
10 months13 human years
11 months14 human years
12 months15 human years

Related

Age shown for a 9-month-old dog of average breed size.