Why your dog isn't the age you think

Aging is certain biological metrics like efficiency, consistency, and general wear and tear to macro and micro features and processes.
In certain rare cases, someone is born with a condition that accelerates or decelerates the decline of these metrics.
All sorts of factors go into this, but most animals, and some humans have more complete and diversified DNA which provides them with longer telomeres which act like a buffer that slows down this process, leading to a more consistent, linear decline.
This is why dog breeds that are more inbred tend to have a similar accelerated decline to humans.

Chronologically, I'm 36, but according to some recent doctor's visits, I'm still biologically in my early teens and I'm just progressing at a more linear rate.
The only thing I can think of leading to this would be the fact that I absorbed my triplet sister and some of my remaining twin brother while I was in the womb. I might just have some backup DNA in parts of my body. Only issue is it's lead me to develop tumors a few times.