That does not makes sense to me. High-end headphone manufacturers want as many people as possible to buy their phones, of course. Older people can not hear very high frequencies, true. However, most people have already lost a lot of higher frequency hearing in their early 30s, especially if they spent their teens listening to too loud headphones. (Maybe you are very young and "mid-to-senior age" means thiry to you?) That means that a substantial portion of ALL adults can't hear to 20 kHz. Not that there is that much to hear in music up there. When I go to a live concert, no one boosts high frequencies for me. In everyday life, no one boosts high frequencies. That is the sound I'm accustom to. If a headphone boosts high frequencies, it will sound unnatural to me and too bright to you.
Well, it was just my hypothesis. I think that we can see how the expensive phones frequencies look and just compare to mid to low price phones, especially of DJ and bass head style. In that case, probably expensive phones will have more natural, balanced sound with better higher frequences, maybe not boosted, but sounding sharper in HF. This will be more premium sound rather than derived by boosting bass, though it may sound a bit dull, of course.
I will try to find such frequencies chart for low price and expensive phones and it can easily proved or rejected.
This chart, with phones selected by me, shows frequencies chart. Interestingly Momentum is truly a dark phone, but HD800 has higher HF than all, especially HD202 (a street DJ) phone and being most expensive, looks more balanced with higher HF of all selection.
HD202 a cheap phone has boosted bass same as more expensive M50, and its HF are less, proving that its younger generation oriented.
M50 has higher HF than all, except HD800, despite being labeled a bass phone - it is more expensive and higher class than HD202. It can be liked by both buyers of expensive phones and younger generation. Very universal, with clear V shape.
The odd one is Momentum though. Momentum seems to be strictly for younger buyers who prefer more bassy sound, and otherwise, in HF it resembles cheaper phones like HD202.
Other than Momentum, my hypothesis stands.