[Haul4ss]

This is a good question to ask regardless of your career. It's a combination of factors: specialization narrowing the range of possible jobs, experience tending to command a higher salary, and flat-out age discrimination.

You will likely have peak earning years, and that means earnings will decline post-peak. For most people this is true, not everybody.

If you know this is a likely pattern, you can do something about it. Namely, live below your means, invest, bank raises, keep a lid on lifestyle inflation, and accept that some day you will take a job that pays less than your previous job and that this change should not be ruinous.