This age might keep increasing because those who try too late won't reproduce. So it's passive selection for longevity.
Maybe immortal humans give you a better bang for the buck.
New humans allow for changes in DNA to fit a changing environment (immortality doesn’t - hey, you get my drift)
Thinking of the people’s throughout history who shrunk to be smaller due to poor nutrition or unstable food source let’s the human race adapt pretty well to a whole host of issues. Immortality (unless it’s accompanied by some pretty impressive technology from the future) doesn’t.