There have been several SciFi takes on this. Three stick out to me beyond Heinlein’s tales of Lazarus Long. These are Niven’s Boosterspice in Known Space, Blish’s antiagathics in the Cities In Flight, and Weber’s Prolong in the Honorverse.
My memory on Cities In Flight is poor, but I think the antiagathics were rare and kept only to the upper class so it has limited effect on it’s society other than envy of the upper classes.
In both Known Space and the Honorverse there is a tendency for careers to be MUCH longer. What would have been generational wealth tends to be personal wealth over time. Prolong gets you 200-300 years in very good shape.
Boosterspice is unlimited, Louis Wu is celebrating his 200th birthday at the start of Ringworld and hangs around MUCH longer(potential spoiler for a 30-50 year old series 🙂 ). There is a hint in a later Known Space story that, over time, Boosterspice also makes Humans VERY risk averse (though not quite Puppeteer risk averse).
In the Honorverse Prolong also seems to extend the period of fertility so 100+ year old couples can be seen having children much later in life. I do not know about boosterspice.
At the time of Ringworld, Earth is still run by the UN and the birthrights system, but little is said otherwise. That said Teela Brown had not yet had boosterspice when she (presumably 20 something) heads off to the Ringworld(again potential spoiler). This might suggest that although extending life the effect on fertility is either negative or irrelevant so reproduction is limited by the normal span of ~ 40 years.
There’s also the spice on the Dune series though I don’t remember longevity being attributed to it. And then, there are the auto docs that seem to proliferate through so much of SF. If you happen to stumble upon one of these, let me know because I have desperate need of one right about now. BTW: I can damn near quote every Niven and Pournelle book verbatim from memory. It’s very easy in theory to boost human life span to any figure you’d care to name by boosting their velocity to 99.999%= of C or tossing them into a black… Read more »