In his heyday, he was a sex symbol for millions of screaming teenagers.
But as Paul McCartney famously foresaw in his 1967 song When I'm Sixty-Four, such physical attractions rarely stand the test of time, Mail Online reported.
As he shuffled along the beach in Mexico with his girlfriend Nancy Shevell, the former Beatle's only connection to those glory days seemed to be his swimming trunks, which looked faded and shapeless enough to have been in his wardrobe since then.
At 66, and having just emerged from a bitter divorce from Heather Mills, Sir Paul could argue he has every excuse for a less than perfect appearance.
But it seems that, having found love again, he is still young at heart. He and Miss Shevell, who have been dating for more than a year, held hands and laughed as they leapt over the waves in the New Year sunshine.
The 48-year-old New York socialite, who is vice-president of her wealthy family's firm, showed off a sleek and toned figure in her halter-neck bikini.
McCartney was first seen with his current girlfriend in 2007, while his divorce was being battled out in the courts.
Miss Shevell is legally separated from her husband Bruce Blakeman. They have a teenage son, Arlen.