Not disagreeing about ageism - been there, done that and the t-shirt was wrinkly.
But. My mother was in her 80s and even before the dementia she was, as she had been her whole life, as dim as a Toc-H lamp. My Dad had been a very bright man, but by his mid-70s he was unable to adjust his way of doing things, to the extent that I had to take over a lot of his dealings with agencies, banks and so forth. His 'wisdom' consisted of long, rambling, often repeated, anecdotes. Not every old person is wise - most of them are still as dim-witted as they were when they were young. I know. I'm. one of them.
Where ageism needs to be fought is at the other end. So many bright, capable young people are delaying marriage and children until their late 30s, and having one, perhaps two, children. Because they have to establsh their careers while young enough to do so. To maintain their careers, they must settle for a miserly few months parental leave before diving back into 60-hour weeks. They leave the poor youngsters with nannies and carers who, in the main, are unable to provide the spontaneous stimulation ad support to be gained from interacting with bright people (by and large, the 'caring professions' do not attract people of high intellectual attainment). Thus the supply of bright, capable young people for the next generation lessens year by year. The education system, with its laser focus on passing the next test to maintain the schools' status and funding, does not help.
We need to acknowledge that young people have far better and more important things to do than work. That promotions are things belonging properly to those with maturity and experience. That high-pressure working environments benefit nobody except the would-be Hitlers that manage them. We need young people coming out of University, getting married (or not, to taste) and being givne the time and space to properly raise two or three kids to at least 11 before having to worry about career advancement. I'm not saying don't work, but being able to work sensible hours, from home if wanted, being paid enough to have a decnet lifestyle, and not have to think about climbing the ladder until their mid-thirties at least.
As for the old folk - they do cost billions in care, because every year beyond sixty means more bits dropping off, more pills and potions, more operations and hospital stays, cleaners, carers, care facilities and so on. I wake up every morning and everything hurts, and if something doesn't hurt it's because it no longer works! Our bodies and minds weren't built to last that long! Get the health fascists off our backs! Let us have our fags and booze and red meat and butter and sweeties. Let us get back to dropping dead in our sixties and seventies while we still know who we are and can recognise our kids!
Queror, ergo sum.