How old is old? That depends on how old you are, for as you age you will nudge that number upwards. A recent German study asked people over the age of 40 that same question eight times over a period of 25 years, and it found “old” gets older as we age. Of course it does. Would Paul McCartney, fit at 81¾, choose 64 now as the time he’d need feeding? Jumpin’ Jack Flash at 80 is as lithe and frisky as ever, but only a halfway Dorian Grey, young in limb, but a face as raddled as that portrait: is Mick Jagger old yet?

I am 77: I and my friends contemplate our age all the time. How old are we, exactly? I can feel like Methuselah, mentioning to some bright young spark that the first election I covered as an Observer reporter was 1970, or that I remember the old king’s funeral, or that I had a doll’s ration book (sweet rationing lasted until 1953), or how the great smog of London of 1952 that killed 4,000 knocked me down with bronchitis, inhaling Friars’ Balsam under a towel. That’s old, isn’t it?

But I’m happy to reject other people’s judgment of age, certainly if it comes from social media trolls. Last week one man posted “God, are you still around? I thought you’d been in a home for years.” Another, “Oh, Polly’s still alive then?” and a third wrote: “Retire already.” Enemies’ abuse mutates from stupid woman to stupid old woman. Even friends, such as the estimable Roy Lilley, last week blogged a compliment (I think), reading: “She might look like a kindly granny who’d make you fold yer pyjamas and sit-up-properly at the tea table. But … if she was a sports star, she’d be a cage fighter.”

When I was 18 I had a (bad) novel published in which the old and dull were in their 20s. Now, I think “old” only applies to the seriously infirm in brain or body. If alert and nimble, you don’t count as old, do you? But certainly not as young. The young are different, in another time-zone, unhindered by experience that curbs enthusiasms with, “Oh, we tried that before and it didn’t work.”

At our age you think about death a lot, calculating how many years, how many Christmases left and wondering if your youngest grandchild will remember you. Contemplating cupboards full of clothes, you think: perfectly serviceable enough to see you out, don’t need any more, do you? And there’s no use wishing you aged as beautifully as Helen Mirren – there never was. My generation of wannabe actors at the National Youth Theatre never forget the day she knocked away their foolish delusions the moment she stepped on stage.

I might say bravely that I am not afraid of dying, after two run-ins with breast cancer: I am only terrified of dementia or exiting through a torture chamber. But I’ve no idea if that’s true. Until you hear the knock on the door, you can’t know if philosophical wisdom holds up. I’ve been surprised by the deaths of others, the stoics and the frightened clingers-on.

You just want to keep going. Blessed with a large beloved family, four children and seven grandchildren, I pause more often to think of my good luck. At my age, you have shed excruciating youthful anxieties about how things will turn out. I’m turned out, and this is as good as I get. I will not improve with age, nor grow wiser or nicer. I have no bucket list. Last year I even wrote my memoir.

If anything newsworthy befalls you in the street, you will be called “grandmother” or “pensioner”, a meaningless identifier when pensioners are even more socially divided than the rest. Pensioner politics are perplexingly contrary: fewer of the old are poor than the general population, but it’s still 2 million people. The low-paid risk growing too ill to work, falling into the benefit abyss between job and a rising pension age. Yet the old are also the wealthiest, my generation reaping unearned bounty from house-price inflation, blocking the young from buying. But 1.6 million pensioners have an unmet care need and many die waiting, with no government daring to skim property wealth from the old to fund universal social care. Pensioners are powerful voters, installing one Tory government after another. The young should wish us all dead, though polls show them amazingly magnanimous.

Geroscience may keep us alive, but clogging up NHS beds with multiple miserable morbidities. Could it keep us healthy longer, then kill us off fast? Monday’s landmark debate in parliament reflected the two-thirds who want the right to die. Last year, Sima the lab rat became the longest-living rat in history. What was her sinister elixir? The blood of the young, which reinvigorated her organs. By living too long, will we vampire the young? I don’t know how old is too old, but I intend to recognise it when I get there.

• Polly Toynbee is a Guardian columnist

Source: theguardian.com