Big part of why programming is front loaded is that it's an incredibly new field. The entire field hasn't existed for more than 70 years. And that was if you count "Niche academic field that a few dozen mathematicians knew about" as the start.

It didn't become like a job job until what, the mid 1960's? That's 60 years ago.

And the number of programmers is doubling every ~5 years. Of course it's front-loaded with young people! The people who have been doing this for the field's entire time of mass popularity (1980's onwards imo) haven't even had time to get proper old yet.

But also: The more experienced you are, the more your biggest value isn't in banging keys on the keyboard. A company would much rather leverage your thoughts and opinions and that may look a lot more like technical leadership than programming. Even though it's still engineering.