Yes, I'm referencing the title of the novel, Childhood's End. But it's true. If we lived 1,000 years, we couldn't have two children per-woman every 40 years -- we could only have two children per-woman every 1,000 years. That would yield a minuscule number of children at any time. A life expectancy of 1,000 years would require finding a way to extend fertility from ~35 years, otherwise many opportunities to reproduce would be missed completely and fertility would drop well below replacement rate, furthering the end of childhood.
No, we can have immortality, or we can have children, but not both.
I can't imagine a life without children. So I choose mortality. I want to die (in time) so that my children may have children. And my children too will have to die (in time). It's just how it has to be.
But we can talk about what would be a good life expectancy. 200 years would be fine, provided the first 160 of them one could have a young body and mind. And provided we can find a way to not get too bored :) Even 1,000 would be fine provided our bodies and minds stayed young for 850+ of those 1,000. In any case, I don't want to live 120 of 200 years in an old people's home.. Who would?!