One "dog year" is not equivalent to 7 human years. Dog's age at various rates, depending on their size.
Dog's age at different rates compared to humans, but the simple rule of 7 dog years to 1 human year is far from accurate.
If humans aged seven times slower than dogs, then many of us would be able to reproduce at age 7 and live to be 150. That's not the case.
The reason that dogs can reach full sexual maturity after only a year is that our canine friends age faster during the first two years of their lives than humans do.
Even this general statement is slightly off since smaller breeds tend to mature faster than larger breeds.
Compared to humans, dogs age more quickly at the beginning of their lives and slower toward the end. Therefore, calculating your dog's age relative to yours is a bit tricky, but luckily it's possible.
Since smaller breeds tend to live longer than larger breeds, it's important to calculate your dog's age according to the right category: small (20 pounds or less), medium (21-50 pounds), large (51-90 pounds), or giant (over 90 pounds).