The brains of young people have a some plasticity, and that is surely a goal of reversing aging.

It may be that as things are forgotten, the cells and connections that made up those memories will be used for new memories.

When the quality of life drops even lower for the masses of humanity and hunger & disease take millions of lives daily, someone will have to decide...

Sez you. I despise the mindset that concludes "someone will have to decide", with the usually hidden follow-on "and enforce it". Moreover, it's far more likely that individual choice will prevent that condition from ever happening.

You seem to be assuming that the treatments that lead to extremely long life will be secrets, beyond the ken of a basement chemist or small organizations that want their own. Governments are currently unable to stop meth and crack labs, do you really think government will be able to stop much more valuable life extending substances and procedures?

Technology advances, and long-life treatments are unlikely to be single ingredient. It's reasonable to think that some aspects will be available at a reasonable price, and that Joe Sixpack will be able to buy another 150 years, even if he can't afford 250 years.

And the odd question of who cleaned the toilets in the super secret invisible mountain utopia. When I ask that one of Rand fans they go all catatonic and recite Manchurian Candidate style: "They were very happy because they were paid REALLY, REALLY WELL"

Did you miss the passages in Atlas Shrugged where various heroes endured substantial physical hardships? It looks as if your prejudices blinded you to those sections. The nuisance of toilet cleaning is nothing by comparison.

No Objectivist would say that a character was happy because he was paid well, but that is the sort of thing that an ignoramus or liar would claim. Rand was explicit about the need of a person to do valuable work.

What you see as "One-dimensional characters" I see as characters whose lives mean something.

Atlas Shrugged is about the consequences of principles. If characters don't have consistent principles (what you call one-dimensional) then the tie of principles to consequences is weakened or broken.