Will some aging damage turn out to be "long flu"?

Sure, maybe. Colds, too.

It's possible, but keep in mind our standard of care for the flu was/is a lot better than for covid. There's all the stuff that was basically grandfathered in that you can take for the flu that you'd not get if hospitalized for covid, especially in the early days.

In many places, steroids. Antibiotics to prevent secondary infection, and antihistamines to help inhibit the autoimmune response/"Cytokine storm." Also, in the old days there was a pneumonia treatment called NAC, that's helpful for both covid and long covid, but not Standard of Care.

(Also note the secondary infections are supposedly one of the main triggers of the cytokine storm.)

In case you missed it: https://news.ycombinator.com/item?id=37789679