Sounds good.

Oops! Now you have abolished children!

Several possible solutions come to mind. A ridiculous solution, which would still be a tremendous improvement over the status quo, would be to institute a Logan's Run policy where you get 100 years of good health and are then painlessly euthanized. But really, I think concerns like that are analogous to the doomsayers 120 years ago who predicted that given current trends New York would be waist-deep in horse manure by 1950. More likely, I would expect a temporary drop in the birth rate, while we get serious about colonizing space (which we should do regardless, on the egg/basket principle).

In summary: changing the nature of life expectancy will change the nature of our demographic weirdness, but is unlikely to produce anything less complicated.

Things would be different, yes. And given that right now aging is responsible for an impending fiscal train wreck, as well as incalculable suffering and destruction of human potential, we badly need something different.