For a lot of guys, 40 is an age where the body starts to go down hill. Hairs go grey (if there's any left), it's harder to stay in shape and your two veg is trying to make friends with your knees.
But there is one thing in a man's control: style. Just because he hits the milestone age doesn't mean he has to hop into a pair of corduroy trousers and a cardigan and retreat into the cliched man shed.
Although you might not have hit that age just yet, we're here to argue that you should celebrate getting older, and take notes from these guys who have only gotten cooler as the years have marched on.
From Casino Royale to Hannibal, the 50-year-old Scandi actor's career has only skyrocketed as he's gotten older, most probably down to his impeccable style and slicked back, grey tinted hair.
Anyway, what is it with Scandinavia? If they're not producing delicious meatballs, beautiful people and avant-garde brands, they're exporting incredible acting talent. Is it something in the water? The limescale in London just seems to be producing graphic designers, Youtubers and vegans.
Jude Law may be 43, but he has swagger of a teenage boyband member and the lothario status to match. Whether he's at Wimbledon or on the red carpet, his tailoring game his always spot on, and he's not afraid to go bold with his colour choices.
Getting someone young to do a collection for Superdry? Nah, millenials are awful. The brand's choice to pick 44-year-old Idris was a brilliant one, as every mans wants to be like the 6'2 East Londoner.
And hands up for Idris being the next Bond *raises both hands and feet*. The title doesn't belong to a young buck, it belongs to an older chap, one who can portray angst and strike fear with a single glance, and if you've seen Luther, you know he can do both.
Like the inevitability of death, you knew Beckham would be in a feature about older gentlemen. He's an easy one, but one that needs to be mentioned. Motorbike enthusiast, Belstaff model and trendsetter still at the age of 41 (oh, and footballer), golden balls is only getting better with age like that posh whisky he promotes (not printing the name, he's got enough money).
A lot of guys post-40 stick to timeless staples such as navy suits, bomber jackets, slim jeans and darker colours. Not 56-year-old Nick Wooster, New York's most stylish brand consultant who's held high positions at Barneys, Calvin Klein and Ralph Lauren.
Wooster constantly challenges the boundaries of men's fashion, making him one of the most photographed men at Fashion Weeks the world over. But he never looks ridiculous like all the art school kids do in their overpriced neon streetwear, he pulls it off because he's not wanting to show off; he genuinely knows his style and how to wear with eccentric clothing with confidence.
He might be Sherlock's sidekick, but in real life Freeman takes centre stage in terms of style with his Sixties mod aesthetic, pulling off double breasted pinstripe suits without looking like a stereotypical Italian American gangster.
Thought all models needed to be chiseled, under 20 with a six pack and six brain cells? Not according to Prada, who put legendary 58-year-old film star Gary Oldman at the front of its autumn/winter 2012 catwalk show in Milan, dressing the Leon actor out a regal black double breasted coat.
You definitely couldn't wear this in your twenties, because you'd just look like a really wealthy emo.
You thought they were like unicorns, didn't you? Well, they're not, they actually exist. It's true, men can wear skinny jeans after 40 without looking like they're going through a serious midlife crisis, as showcased by Justin Theroux with his charcoal black pair teamed up with brown suede boots and leather jacket for a premium biker look. Just make sure they're not a ridiculously bright colour and not so tight that they permanently damage anything...
Can you believe that Jared Leto is 44? It almost makes you want to become vegan and do yoga (almost, if cheese and staying in bed wasn't so damn enjoyable).
The Suicide Squad and 30 Seconds To Mars frontman (show off) demonstrates you can wear current trends in your mature years, such as pink and souvenir jackets, without looking like you're desperately trying to cling on to your youth. The trick is to keep everything else subtle, so make sure your t-shirt's plain and jeans are dark.