Since January, I’ve been hobbling around – despite orthotics, lifts and trendy, cushioned Hoka trainers – suffering from Achilles tendonitis. According to my first podiatrist visit, it’s common among teachers, police and NHS workers: people who spend all day on their feet. To me, it’s another intimation of mortality as a big birthday hoves into view. One reason I started teaching is that I thought I could do it into my 70s, without experiencing the ageism so rife in my first career: journalism. But is there now an Achilles heel in my plan?

“All” I have to do is stand up. The great cricketer, Jimmy Anderson (41), pounds in on his run-up, day after long, hot day, to bowl his heart out for England. Our greatest-ever bowler just took his 700th test wicket, the third-highest tally in history and the most by any pace bowler. Like footballer Ryan Giggs before him, to be still excelling as an elite level athlete is remarkable. And it came in a week where the subject of “how old is too old?” – from Joe Biden to Mike Tyson – has rarely been out of the headlines. The subject leaves me confused: cold reality butts up regularly against what I profess to believe.

I once ran a start-up company, advocating for the vitality of over-50s – like a sexier Saga. Octogenarians are a different matter. It’s been a week in which it became clear that America’s choice as next President will be between two men well past retirement age: Joe Biden (81) and Donald Trump (77). My dilemma is that I do not believe in compulsory retirement ages, but it is manifestly clear that neither one of these two elderly gentlemen is firing on all cylinders with the acuity, vim and vigour that they displayed when younger. Is this really the best that 332 million people have to offer?

That said, I almost hate myself for raising the question. We are all aware of how much longer we are living and we all know octogenarians – even nonagenarians, like my late, great Ma – who genuinely fire on all cylinders, at least mentally. Conversely, we also all know ever more older people stricken with dementia and other forms of cognitive decline.

When I worked for Rupert Murdoch, he was a mid-septuagenarian and razor-sharp at analysing balance sheets, if not entirely au fait with the then-new digital world in which we were operating. As an example, he had just bought MySpace for $580m, only to sell it six years later for $35m. Again, that said, I kick against the generalised dismissal of so many older people who work in advertising and media as not being “digital natives”. Murdoch (92) has announced he is getting engaged again. Good for him.

Elite athletes are mostly past their best in their late 30s, but not Anderson, Giggs, Martina Navratilova, Tom Brady or LeBron James. However, is anyone really comfortable with news of Mike Tyson boxing again, aged 58? Politicians and business leaders go much deeper into their 80s, but name one at their best in that decade. It’s sweeping generalisations that are ageist, not individual cases. A newly feistier Biden has even launched a new TV ad joking about his age. The trouble is in this case: it’s funny, not funny!

@stefanohat