The issue here is not a radio issue but a marketing one. Nearly all large advertisers restrict their campaigns to the people who represent the most sales and profitable sales.
The main reason why they don't target those over 55 is that the older most consumers get, the more habit-driven they are: preferred brands, skepticism and more. They survey to find who buys their stuff, and figure out who the largest groups are.
A good example of highly targeted advertising is seen with Subaru cars.
Here is an example of how they work and how tightly restricted it is:
Focus groups helped identify 5 core groups: engineers, teachers, health-care professionals, outdoorsy types, and women (who identified themselves as head of household).
– Subaru created strategy and messaging for those 5 groups. For medical professionals the all-wheel drive could get them to hospital in any weather. For others, Subaru could handle dirt roads; for lesbians, it fit their active low-key lifestyle. Let’s not forget, this was during a time when very few companies would advertise to the LGBT communities. After launching the campaign, they would get angry letters but quickly realized, those people weren’t Subaru buyers in the first place.
So what affects radio is essentially "where the money is". That concept worked for bank robbers, and it drives radio.