Exactly. It is far more fantastical to imagine such lifespan improvements resulting in a planet of crypt keepers than one of external youth. What magic do you expect would keep such people alive?
You could imagine entirely curing cancer, heart disease, frailty and infection but not brain degeneration, for example.
Curing everything else except frailty also seems invidious, though with sufficiently good brain-machine interfaces perhaps that would be less of a problem: you can just float in anti-impact gel from 100 and 200 and mentally roam the wreckage of the internet! If AI takes over knowledge work, how you pay for your life support and data connection may become an issue.
I'm not sure that's a foregone conclusion. Loads of interventions put extra pressure on other body systems (often, but not always, the liver and kidneys). Sometimes to the extent that even if you may "manage" the original complaint, it comes at a substantial cost to overall health. And heart muscle is pretty special anyway, so it's quite possible it's a separate treatment to skeletal muscle problems.
And pretty much any system failing can kill you so if long term life extension comes from targeted treatments per problem, you need to hit bones and cartilage, muscles, skin, nerves, brain, GI tract, kidneys, liver, immune system, endocrine system, lungs, etc etc, but also not overstress any one with the treatments of the others and also handle almost-inevitable cancers.