Average age 40, as you said yourself. And then as the authors of this paper find, "Risks were greatest in, but not limited to, those who had severe COVID-19."
Framing an "average age of 40" as "an older demographic" seems a bit misleading, as the average age of human beings in America is 38. We're not talking a few sickly senior citizens here (which, even if we were, I wouldn't feel justified in writing off, but it's not).
It doesn’t matter if these longer-term symptoms affect some number of people outside that older, frailer risk group. There are always statistical outliers. If the amount of younger, stronger people affected by these symptoms is small, then that weakens the case for maintaining restrictions after vaccination of the most at-risk groups.
This issue seems to be important to you personally and to others whose concerns may or may not be reasonable, but I don’t believe it will be important to most of society as vaccinations roll out and the Northern Hemisphere spring and summer are upon us.