Bruce Sterling’s /Holy Fire/ is on this topic:
"Set in a world of steadily increasing longevity (gerontocracy), a newly rejuvenated American woman drifts through the marginalised subculture of young European artists while dealing with the implications of posthumanism.”
"Holy Fire is the story of an old woman who has gained a second youth […] and who has an ontological transformation as a result.” https://en.wikipedia.org/wiki/Holy_Fire_(novel)