Well we are talking about a universe where designer babies (heck species), artificial wombs, etc. have existed for hundreds of years but there have been no real advances on the anti-aging front aside from reversible cryonics (yay!) and clone-body transplants (boo!). IIRC the lack of real anti-aging tech was hand-waved as being due to not enough people caring to fund the research because clone-body transplants work just fine for those few jerks that want to live forever badly enough.

But then again, I seem to recall that in one of the earlier books Miles was able to use his youthful appearance to trick someone into thinking he had access to a new technology for rejuvenation. Clearly there was some interest. Apparently curing aging is just really hard in this universe.