Are you sure about that?Hearing loss with age is perfectly normal:
"Whereas a person in their twenties will be able to hear up to 17,000Hz or more, by their thirties this will have declined to about 16,000Hz. By the time an individual is in their 50s, their hearing range will usually have declined to around 12,000Hz."
This is often seen with the "cocktail party effect" when you can't hear conversations very well in a busy room.
I think any 'cocktail party effect' would be more down to a lack of lower frequencies for those affected.
True, sibilants give speech its intelligibility, but 12kHz more than covers all speech.