The entire world population is eventually going to top out and start declining, but that may take close to a 100 years or so.
In the meantime we are doing much better than most advanced countries in the population increase area because of our comparatively liberal immigration policy, along with our de facto support of illegal immigration.
There are a lot of reasons why people not born here might want to settle here: lots of coastal property, varied climates and topographies, decent economy, generally free, etc. So if and when we need to entice young people to move here to support the old folks, we will be able to do so.
It would be nice if the people we enticed here were people who could support themselves and represented a true slice of humanity and not a rather narrow slice of those who happen to be living next door.
“The entire world population is eventually going to top out and start declining, but that may take close to a 100 years or so.”
Try 20. The UN’s low population estimate is optimistic, and assumes that nations with negative fertility rates magically trend upwards.