Oh of course. Heck, we have direct evidence that some campaigns lasted years and years. Totally true. But, yeah, as a normative among the broader audience?
Although, I will walk back something I said earlier. Peak 80's D&D absolutely could have been selling best among college age students. Of course, let's not forget that college age is 18-21, so, actually pretty much dead on the same as what D&D has always pegged itself at. Actually, that's a bit younger than what most evidence points to in 3e days. After all, Paizo/Dragon did a couple of reader surveys and found their readership was always around the 20-24 year old range. A band that never changed.
In Dragon 62, in 1981, their reader survey pegged readership at 95% male and 16 1/2 years old. And, on average, had only been gaming for a couple of years. Not really surprising if they were only 16 or 17 years old.
Again, I really have to ask, where is ANY evidence that D&D players were older? Other than maybe in the early 70's I suppose. Certainly after 1980, is there any evidence that D&D players weren't high school or college age on average?
Every piece of evidence I've ever seen - from the scene in ET (and the obvious link to the scenes in Stranger Things) to the cartoon to the advertisements from TSR on the TV, to comic book ads. Nothing even remotely suggests that the target audience for D&D wasn't teens or early 20's.