They colonised Facebook. Then they discovered emoji, and boy did they start to deploy them. Now, parents in midlife and upwards have come for Instagram - potentially threatening its kudos and all that it stands for.

When social media historians look back, they may pinpoint Sir Mick Jagger as the man who brought about the beginning of the end. Sir Mick, who at 74 has managed to remain on the right side of tragic for longer than anyone thought possible, has shown us that even he is not infallible. For proof, look no further than the Insta feed of his 19-year-old son, Lucas. It is here, buried among the many comments on the teenager's pictures, that Jagger has exposed his "embarrassing dad" side.

"Looks like fun. Ha!" he writes beside a photo of his son posing in sunglasses. "Watch out for the water," he jokes - hilariously - on a picture of Lucas paddling in the surf. "Cool pic," he observes about another. Cool pic? Is this some kind of joke? We're talking about the man who, for more than half a century, has been a rock 'n' roller. If even he can't help himself writing cringey dad comments on his son's social media, then what hope for mere mortal fathers?

More pertinently, however, what hope is there for Instagram? The reason we ask is that the three stages of cool are well-established: first, the thing in question (fashion trend, music genre, website, whatever) starts off as niche, preferably subversive and countercultural, too. Then, as it gains in popularity and profile, its cutting edge appeal swiftly and predictably diminishes. Finally, it becomes so mainstream that you've started to wonder what the fuss is about and before you know it you have signed up yourself, much to your children's dismay. For them, thereafter, it's game over; the cultural moment has passed; the thing that was niche becomes ubiquitous - and if they care about retaining their street cred, your kids will sell up, get out and move on, quick.

So when fathers of a certain age get involved - even those like Sir Mick, with more panache than your average - it's rarely a good sign. Start me up? He could be more likely to finish it off, if we're speaking of Insta's prized youth appeal.