In my experience, it's been the complete opposite. The very experienced engineers that are actually willing to use top of the line tooling are much better than they were before, including those that are over 40, and over 50.

Part of the practical degradation of traditional programmers over time has always been concentration and deep calculation, just like in chess. The old chess player knows chess much better than a 19 year old phenom, but they cannot calculate for that many hours at the same speed as before, so their experience eventually loses to the raw calculation. Maybe at 35, or at 45, but you are just not as good. Claude Code and Codex save you the computation, while every single instinct and 2 second "intuition", which is what you build with experience, is still online.

It's not just that it's a more fair competition: It's now unfair in the opposite direction. The senior that before could lead a team of 6 is now leading a team of agents, and reviewing their code just as before. Hell, it's easier to get the agent to change direction than most juniors around me, which will not be easy to correct with just plain, low-judgement feedback.