But is a life with confusion, even partial loss of memory, unproductivity, and dependence genuinely a life?
Life is about nurturing children and enabling them to live a ‘normal’ life.I am not a pediatrician. 

In terms of human behaviour: I’d like to hope, as one of John Wyndham’s protagonists did in Trouble with Lichen, that it might actually encourage people to seek more meaningful lives, and to plan on a longer timescale.  But for many, it might also be a very daunting prospect to keep on going, and going, in our changing world.  Especially with what this would do to the pension age.

In terms of medicine: taking a history would take rather longer.  And everyone would have even more co-morbidities than they already do.  And since so many different bits of the body accumulate different types of damage at different rates, this could well mean we’d all end up living with one or another disease of ageing, eventually, be it osteoarthritis or cancer.

Finally, in terms of human population issues: while we’re imagining possible futures, a lack of living space on earth  could well give us a great deal more impetus to seek to build new lands, beyond our home sphere.  Might longevity be what finally drives us to terraform Mars, in this century or the next?  Or populate the oceans?  As challenges go, the former at least is probably up there with beating old age itself…

PS  There’s a minor typo in the 8th paragraph, with the second use of the word “old” in this sentence: “   Diseases of old age (which is most of them) kill 50 million people a year old worldwide and these will be preventable deaths like any other.”