They wouldn't have to be in a hurry, they'd just have to be interested - if everybody has one kid at 150 years old, that's still 50% population growth per year

They wouldn't have to be in a hurry, they'd just have to be interested - if everybody has one kid at 150 years old, that's still 50% population growth per year when it stabilizes. It's certainly possible that much of the impetus driving us to want children stems from our own mortality, so maybe many people wouldn't want kids after long life became the norm. Or, maybe the psychological imperative would decline enough that some sort of lottery system would actually be acceptable.