Ever since 1979, Billy Connolly has been 37.

His birth certificate suggests he will be marking his three score and tenth birthday this November but no matter, for as the bawdy bard explained in a recent interview, he is happy to grow old, so long as he doesn't need to grow up. Hence 37, his mental age by his own eccentric yardstick.

The context is his latest film, a gentle comedy on the theme of ageing well. Directed by fellow age-defying pensioner Dustin Hoffman (75!), Quartet is about four retired opera singers living out their declining years in an idyllic care home for superannuated musicians. It balances humour with a tender pathos that is already drawing comparisons with last year's surprise hit on a similar theme, The Best Exotic Marigold Hotel. Connolly plays Wilf, who, following a stroke, says whatever crazy thing pops into his head. Could this be the very definition of typecasting?

This week he has been warning against retirement on the basis that it induces "brain rot". (The cast of Quartet largely consists of retired musicians and opera stars, playing characters just like themselves, which seems a novel way of keeping the old grey matter moving but one sadly unavailable to the rest of us.)

Connolly cites trips home to Glasgow where he meets old schoolmates who have "voluntarily become old". "They've gone for the old-guy haircut and the old-guy sports jacket and that terrifying little half a raincoat that they wear. And they call me Peter Pan," says Connolly with his black jeans, shoulder-length hair and devil-may-care jauntiness.

As an incipient retiree, complete with bus pass and senior railcard, I'm drawn to this subject. I feel perpetually torn between wanting more time to devote to hobbies and family and a nagging fear that, without an office to come to, my life would lose its structure and purpose. After nearly 35 years with The Herald, who would I be without it? Sometimes we wave off old colleagues with cards and gifts, only to see them creeping back, begging for shifts after a month or two aimlessly floating about.

The image of retirement is not helped by all those people who have left it too late to shift those surplus stones, plodding grimly on treadmills at the gym. Or those old dears who hover like moths round a flame, close to the supermarket shelves where they chuck spoiled and time-expired food. I'm particularly painfully aware of a group of miserably poor frail elderly women, who retired before recent reforms and don't even qualify for the full state pension because of inadequate National Insurance contributions, sacrificed to years of caring for children or their own elderly parents.

Of course, this is not the whole story. As the latest figures from the Office for National Statistics demonstrate, there is a widening rich-poor gap in retirement, with those in the leafiest areas likely to enjoy 13 years of good health after 65, compared with less than eight years for the poorest. At the launch this week of an anthology of the writings of former editor of The Herald Arnold Kemp (who sadly died in harness), it was encouraging to meet former colleagues who didn't look a day older than when they retired a decade ago.

Predominantly, they seemed to lead a portfolio existence, dividing their days between volunteering, modest income-generating activities, gardening, sport, travel and grandchildren. Surely a prospect to be relished, not feared.

As part of a post-war generation that has rewritten the script for the first six ages of man (and woman) as we have passed through it, there seems no reason not to reinvent the seventh. Once I pledged to see out my allotted span playing fiendish games of Scrabble with a gay friend in a small nursing home with roses round the door, run by a kind matron with pink cheeks. I haven't changed my mind.

Variety magazine reports that Quartet "offers a spirited portrait of souls who, when the final curtain-call comes, intend to go singing, dancing and swearing into that good night". So come fellow babyboomers. Let's grow old disgracefully.