Most 'youthful' old person I've ever met was my best friend's great-aunt, the
older
sister of his paternal grandfather (who was in his late 80s at the time, so she was probably at least 90).
Flew from Kansas to NC for a grandneice's wedding (best friend's cousin), declined to be picked up, rented a car at CDX, drove 50 miles to the venue, and the last time I saw her she was walking barefoot across the parking lot to her rental car because she said her shoes hurt.
I am the infinite stairwell between integers.