I think there are two other ways to interpret this, within the reality that closed accounts still count toward AAoA:

First, if you "keep them open and active", they can continue to age, and will not fall off your report after ten years. I've found that it is very helpful to have several no annual fee cards that are continuing to age longer than 10 years. It buffers the impact of new cards even more, compared to closed accounts that can never age more than 10 years.

The other factor is: FICO has a small element regarding the age of the single oldest account on your report. So if you only close accounts right after you open them, that factor will never age more than 10 years.