I don't think that the full story. The bottom line is that as you age, you will inevitably start making different trade off's and choices.

As you grow older, you start to truly understand that life is finite, with everything that entails: loved ones growing older, and passing away, you noticing your own body changing as well as you enter middle age, noticing how your own perspective and experience of passing of time shifts (when saying "20 years ago" isn't an abstract phrase, but an experience you lived through), and also noticing how the expectations others have of you start shifting.

That doesn't mean you can't be inquisitive, energized or wanting to continue learning from your own mistakes. I do that all the time, as I understand the importance of learning throughout life ...

... but I'm far more conscious of the value of time and how I use that time shapes me as a person.

Being experienced also means being in control over your time and your life, knowing to set boundaries and keeping a healthy balance between your priorities, and the priorities of others, which also includes the priorities of clients and employers.

Let's not forget that the "tendency for some people to stop progressing" also tends to be used as a strawman argument in order to undercut the importance of the above and push people to change their priorities in ways that may fly against their own self interest.

That's why I've grown weary about generalizing arguments that one has to "progress" without stating exactly why, within which specific context, or within which specific boundaries.