There's a whole world of thought on this. Check out some of Aubrey de Grey's work for starters.

In addition to Aubrey, also Dr. David Sinclair.

...and GSK who payed >$700 MM for Sinclair's company Sirtris (and closed it 5 years later.)

I think we could easily handle it. Most people want to live longer and do more while they're alive. People who parrot the idea of "the shortness of life is what gives it meaning" are lying to themselves and others, in my view. They use that sort of justification as a coping mechanism, it isn't a truly held belief. If it turned out that humans could now live to 500, they'd just update their baselines to be 500 instead of 80 and adjust to the new situation rapidly.

> What would happen if there was somekind of treatment where people could reduce aging process

Probably the first result would be cancer.

I don't think most people have the mental energy for our current lifespans