Can years of wisdom be boiled down to a slogan, asks Oliver Burkeman

When I asked my 85-year-old grandmother if there were ways in which old age had brought her increased happiness, she immediately mentioned how easy it is to get rid of telemarketers. "I'm in my 80s!" she enjoyed scolding a man from TalkTalk the other day, thereby implying it wouldn't be worth his while explaining what "broadband internet" meant. My grandmother knows exactly what broadband is.

But she hadn't really answered my question. I'd been hoping for something profound: a life-lesson born of experience. Maybe the notion that old people are wiser - and consequently happier - is a wishful desire to believe there is an upside to ageing. Still, it's the driving force behind numerous recent works in which the old are pestered for advice - most famously the bestseller Tuesdays With Morrie - and also the book that prompted my grandmother-interrogating: Henry Alford's How To Live, a marvellous new memoir-cum-advice guide based on conversations with oldsters.

There are problems, though, with hunting for distilled insights from the old. First, it's horribly self-selecting. As research, Alford read a book entitled 80, comprising interviews with 80 famous 80-year-olds - but all he discovered was famous people's opinions on how to live. Perhaps others approached life similarly, but encountered only mediocrity, and never got interviewed for books? Or perhaps they followed a different approach and were happier, but not famous. ("To read 80 interviews given by primarily affluent white Americans," Alford writes, "is to have the prescription 'Do something that you love' beaten into your head until you're ready to maim a small animal.")

Second, while there's mounting evidence that older is indeed wiser, it may not be the kind of wisdom easily boiled down to a slogan. Except in cases of dementia, a 2008 review of the academic research found, the typical problems of the older brain - slower reactions, declining short-term memory - may be side-effects of something positive. Age widens the focus of attention: older people presented with problem-solving tests go slower, but do better; they weigh more data, consider more possibilities, and place them in a broader context of experience. Is it any wonder that takes longer? The neurobiologist Lawrence Katz defines wisdom as "a dense and rich network of associations developed through a lifetime of experiences". You can't express such wisdom aphoristically: it is, precisely, the wisdom to know that life's too nuanced to be summarised on a fridge magnet.

Older people are happier, too, according to the "happiness u-bend": both young and old are cheerier than the middle-aged. We don't know why, but it's tempting to speculate that most twentysomethings don't know life's pain, while seventysomethings have discovered ways to cope. Soundbite advice purports to offer a short cut. But if wisdom's derived from density of experience, maybe there is no short cut. Maybe you just have to grow old.

If you insist on a soundbite, I offer Edward Albee's to Alford: wisdom, he suggests, is "finally being able to figure out what you should be worrying about and what you shouldn't". Or this, from my grandmother: "Nobody has any idea how their life's going to work out, do they? But that's probably a good thing."