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.
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)
Son: 64
Son’s transplant of mothers kidney: 48
Typical kidney transplant lifespan: 15-20