When Manchester United signed Zlatan Ibrahimovic in 2016 there was a school of thought that the 34-year-old was too far past his physical peak to thrive in the Premier League.
English football audiences had always had a sceptical view of Ibrahimovic, just as they had of Edinson Cavani, so when he moved to United in the twilight of his career it was easy to suggest they were getting a diminished version of an overrated striker.
Instead, Ibrahimovic was an overwhelming success at Old Trafford, with 28 goals in 46 games in his first season and but for a serious knee injury, his spell might have been extended. But at 35 and with a knee ligament injury to overcome that really did look like the end.
But as Ibrahimovic famously said in the Old Trafford tunnel, "lions don't recover like humans", and he wasn't done at 35, not by a long shot. He turned 40 on Sunday and having initially left United to go to Major League Soccer, he is now back in the big time in Europe, proving an inspirational signing for AC Milan as they try and restore former glories. It's an astonishing story.
Since Ibrahimovic left United at 35 he has scored another 82 career goals and has even come out of international retirement to play for Sweden, with his sights firmly set on appearing at the World Cup next year at 41. His move to Milan wasn't out of sentimentality either.
He joined a club with a young squad that were struggling to find a direction and almost immediately turned them into contenders. He's scored 26 goals in 38 Serie A games, including in his return to action against Lazio last month.
Ibrahimovic's heroics at 40 are just the latest example of footballers going on for longer - and at a higher level - than ever before. United could probably have got more out of the Swede rather than sanctioning his departure in March 2018, but his success at Old Trafford started a trend.
Last year United signed Cavani at 33 and saw him flourish, his energy and industry shaming forwards a decade younger than him and his goalscoring ability honed through years of experience. Having agreed a one-year extension that will keep the Uruguayan at the club once he's turned 35, United went and signed a 36-year-old forward as well this summer.
Cristiano Ronaldo's return was a sensational story but he's done what everybody expected of him, regardless of the advancing years, scoring five goals in six games so far. There have been occasions over the past 10 days when United have chased games with Ronaldo and Cavani in tandem, a strike force with a combined age of 70 but as close to a guarantee of goals as you can get.
Ronaldo signed a two-year deal on his return to the club, with the option of a third, and there's no reason to believe this is a brief stop on a farewell tour. He might be 36, but arguably no footballer in Europe can match the physique Old Trafford saw up close after his late winner against Villarreal.
The Portuguese forward is the embodiment of fitness and his immense professionalism on and off the pitch could add years to his career. He doesn't look like somebody slowing down at the moment.
And as he glances at what he's left behind in Serie A he might see a reason to keep going for another four years or more. If Ibrahimovic can still perform at the highest level at 40, having had a serious knee injury late in his career, then so can Ronaldo.
United were expected to be in the market for a striker next summer and with Erling Haaland certain to leave Borussia Dortmund, they might still be, but the signing of Ronaldo doesn't have to be a short-term solution. As the years progress maybe he won't be able to play every week, but as Ibrahimovic is proving, retirement or retreating from the limelight is no longer a pre-requisite for a footballer in his 40s.
