I have never been able to determine a person's age. Aside from knowing they're a child, adult, or a mature adult (grey hair, wrinkles), I cannot determine an actual age. A 19-year old can look 40 to me, and a 60-year old can also look they are 40.
It would be absolutely wonderful and I would be eternally grateful if there was a term to describe this about myself instead of going on and on describing it.