> population growth & infrastructure that can't keep pace
why would that be a problem? the healthier the older population gets, the more they can work and produce more (instead of "retiring"), and this production includes making more infrastructure (directly, or indirectly via taxation).
Because having it happen all at once would strain many things to the breaking point. If it only extended life by 7 years then we'd have roughly 10% higher population-- on top of normal population growth.
If it became widely available, the second that happened it would be a race to invest in infrastructure and especially higher yield food production-- investments that would need to be measured in large fractions of the world's GDP.
And it wouldn't even add to the viable workforce for a while: this is life extension, not rejuvenation. We're stuck with the working population we have now: People past 65 aren't going to be able to get out there and build infrastructure. Plenty of them wouldn't want to either if they were otherwise near retirement or actually retired: It would require uprooting their entire lives to change tracks.
I'm not saying it's theoretically impossible, just that I see no likely way it would actually happen given the state the world is in right now.
why would that be a problem? the healthier the older population gets, the more they can work and produce more (instead of "retiring"), and this production includes making more infrastructure (directly, or indirectly via taxation).