It might be that people enjoy living without children for as long as possible in the current western economic/cultural climate.

This age might keep increasing because those who try too late won't reproduce. So it's passive selection for longevity.

I think it's passive selection for reproducing in your late teens or early twenties out of bad luck. Even a century ago, your wealth level had a tremendous impact on whether or not your prodigy will survive, so there was an evolutionary selection for social success; with modern welfare state, I don't think that there's any selection bias towards the wealthy.

Or passive selection for not being part of an infertile and decadent culture.

Creating new humans is costly and risky.

Maybe immortal humans give you a better bang for the buck.

New humans replace those eliminated in accidents (immortality doesn’t).

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.