I'd not heard of yeast scarring before, so I researched a bit.
From Replicative ageing and senescence in Saccharomyces
cerevisiae and the impact on brewing fermentations Ageing is the
predetermined progressive transition of an individual cell from
youth to old age that finally culminates in death. Yeast
replicative ageing is a function of the number of divisions
undertaken by an individual cell, and may be measured by
enumerating the number of bud scars on the cell surface. So,
scarring is used as a direct measure of the yeast's age. But
it's not thought that the scars themselves cause deterioration
of the yeast: [...] increasing the deposition of chitin, the
major component of bud scars [...] has little effect on
longevity. but rather other factors, such as genetics, play a
key role in the vitality of the yeast: It has been postulated
that ageing occurs either by a genetic inhibition of
metabolically essential proteins and enzymes, such as DNA repair
enzymes or antioxidants An aged yeast cell exhibits a dist