>20? Maybe. but How about being in the body of a 30- or 40-year old again? I can't imagine any 70-year olds not wanting to have a more "hassle-free" body, all other things being equal.
Nobody is going to pay for your pension forever. Do you really want to spend your entire life working?
Not a lot of people get pensions where I live anymore (or at least, not enough of one to live on comfortably). If you don't want to spend your entire life working, you could save for retirement, same as you (hopefully) do now. A lot of people plan their retirement so that they can live off the returns of their investments without touching the principal. If you do this, there's not much difference between retiring for 20 years versus 200.
I live in germany but I tried to use common sense.
In this scenario our society would be split into two groups if we pay pensions for eternity:
Those who lived long enough to receive their pension. Their body turns 30 again thanks to breakthroughs in science.
And those who never age beyond 30 and so they never get their pension.
The first group effectively gets "basic income" and they probably own houses/apartments so their living costs are quite low. You can either let everyone have pensions or get rid of pensions.
Nobody is going to pay for your pension forever. Do you really want to spend your entire life working?