Next month, Paul McCartney will turn 64, a landmark birthday in a life considerably less ordinary than the one the schoolboy imagined.

But while the idea of Sir Paul mending a fuse . . .as he promises elsewhere in the song . . . might raise a smile now, the fact that his simple teenage aspirations to enduring love and happiness in his old age have been ripped asunder renders 'When I'm 64' suddently terribly poignant. No Valentine, no bottle of wine, no rented cottage in the Isle of Wight. Paul McCartney will mark his 64th birthday suddenly single. The years since he sat at his father's piano and played fantasy retirement may have taken him on a magical mystery tour, but being solo at 64 was never part of the plan.

Worse, there is a sense abroad that the former Beatle has made a bit of a fool of himself. Since the end of his marriage to Heather Mills was formally announced on Wednesday, the I-Told-YouSo brigade has been out in force, but on this occasion, there appears to be plenty of fuel to stoke their smugness.

A quick click on Mills's website reveals a fiercely ambitious, self-obsessed woman who blames the media . . . "people who've never met me" (for the record, this reporter has met her twice) . . . for the fact that she is regarded with a dollop of suspicion by the public and for all her apparent woes.

A Note From Paul on the site makes for particularly uncomfortable reading, as the man who wrote the soundtrack for the second half of the 20th century deals with such weighty issues as whether or not Heather "made" him dye his hair. "Not true. It is true that I colour my hair.

Wow, Shock Horror! I've actually been doing this for many years now with varying degrees of success, but it's my hair, and if you don't like the result I'm afraid it's just too bad, but it's certainly nothing Heather suggested."

It is understood that it was at Mills's insistence that the couple's joint statement this week blamed "the constant intrusion into our private lives" for the break-up of their marriage. For its part, the accursed media thinks it might have been more to do with the constant arguments . . .

she famously threw her engagement ring out of a hotel room window . . . or the 101 other factors documented on the "fact and fiction" section of Mills's extraordinary website.

Whatever the reasons behind the collapse of the McCartney marriage . . . and certainly, friends of Paul's have suggested that storm clouds were gathering for more than a year . . . the next phase of the unravelling is likely to offer McCartney a painful lesson in the cost of loving.

At the time of their engagement, back in 2001, Mills said that she'd offered to sign a pre-nuptial agreement but that the former Beatle had refused on the grounds that it was "unromantic" and they were "too much in love". What happens next will be even less sugar-coated: divorce lawyers practising at the higher altitudes of their craft surmise that the four-year marriage may cost McCartney as much as 300m in a divorce settlement.

Mills's continued insistence that she is not a gold digger may support a smaller settlement, though lawyers agree that McCartney will be down at least 75m for his four years defending Heather from people she's never met. The settlement will include school fees for the couple's two-year-old daughter, Beatrice . . . unlike McCartney's older children, young Bea is unlikely to attend the local comprehensive.

But ultimately, the sorry ballad of Paul and Heather is more a lament for lost love than a salutary financial lesson. In spite of the worldly wisdom thrown up by 40 years at the rock'n'roll face, the idealist who dreamed of a dotage by the fireside with a companion who'd knit him sweaters never really went away.

But the woman who undoubtedly would have still needed him and fed him at 64 did. Simply, sadly . . . and maybe even stupidly . . . it took marriage to Heather Mills for Paul McCartney to realise that his marriage to Linda Eastman was one in a million, a 29-year happy-ever-after unblemished by so much as a report of a raised voice. Maybe Paul McCartney thought all marriages were like that. Maybe there's no fool like an old fool.

Or maybe the teenager who wrote the suddenly heart-breaking line "doing the garden, digging the weeds, who could ask for more?" has finally learnt that money can buy diamond rings and young wives but, just as he predicted many years ago now, it really can't buy you love.