I hope you're correct about the decline, but I fear that you're being overly optimistic.
I've written about this, too. The less ageist you are, the less likely you are, when you get old, to suffer from dementia and pretty much all other age-related health issues, longitudinal studies show.
Ageism is often called ironic because it's a prejudice that the ageist young person will eventually be the target of -- if they're lucky. It's prejudice against one's own future self. But in this piece for the
New Yorker, Tad Friend argues that's not ironic at all, it's the whole point. Ageism embodies buried fears about one's own decline and death.
https://www.newyorker.com/magazine/2017/11/20/why-ageism-never-gets-oldFriend's article came out a month or two after mine. He used literally the exact same sources. Mine didn't end on quite such a bleak note, however.
As for commercials, I think you really need to look carefully at what is being sold, and to whom. Of course you're going to see happy, healthy, active older people if the product being sold is something supposed to keep older people healthy and active.
I remember a particular commercial (I think it was for Ensure) that featured an older couple driving down some highway in a convertible, healthy and happy--and using Ensure.
I work for the company that makes Ensure. Or rather, the Fortune 200 company that bought out the Fortune 500 company I started working for in 2014. Abbott's whole brand theme is "life to the fullest," so their commercials feature people doing things like finishing marathons, peaking Mt. Everest or at the very least just leaping into the air at the beach. (In addition to Ensure, they make baby formula and other health-related products.)
A retired former coworker (mid-60s, I'd guess) got in a bike accident a while back. He's recovering, but he mentioned on Facebook that he'd been taking Ensure. I said, that's great because in no time you'll be finishing marathons, peaking mountains and leaping into the air at the beach. He said that coincidentally during the past year he had done all three of those things. I said, in that case you'd better lay off the Ensure, or you'll be taking up parkour and skateboarding in the X-games.
Boomers are ultra-sensitive to aging stereotypes ("Hope I die before I get old," sang Roger Daltrey, now 74). So they're helping "change the face of aging," which is actually an AARP slogan. They're more active, both physically and at work and other activities, than their predecessors.
However, they also may be heading toward a clash with younger generations over funding SS and Medicare.
Also, boomers are still "young old." The oldest turn 72 this year. People in their 60s and 70s can be quite vibrant and active. After 80 or 85, it's much more unusual. But we'll see.