The math here is a little confusing, but that's an exceptionally long lived organ. For reference I received a kidney transplant from my mother at 16. It lasted 19 years after being transplanted. My mother was 68 when I had to return to dialysis.

TFA mentioned this is very exceptional, it says both that it's the longest lasting transplant this hospital has ever done and that a living kidney donation typically lasts 15 to 20 years. Meaning your 19 years is typical.

The transplant itself was done 48 years ago and the mother was 52 at the time (thus the kidney was already 52 yrs old at the time of transplant)

More simple put, his mother was born 100 years ago and her kidney lives on.

Mothers kidney: 100

Son: 64

Son’s transplant of mothers kidney: 48

Typical kidney transplant lifespan: 15-20