Many people think that staying in good shape is a young man's game, but there are plenty of stars in Hollywood that prove that there's no age limit to keeping fit.

We've decided to take a look at some of the fittest actors in Hollywood who are in enviable shape, no matter what age they are, from whipper snappers in their 20s, all the way up to action stars who are still ripped well into their 60s.

Zac Efron - 27

Having started out in the teeny bopper High School Musical franchise for Disney, Efron has quickly grown up on screen and now has the physique to start playing the action roles those lottery winning genetics implore that he should. We've chatted to Efron a few times over the years, and the actor has bulked up considerably in a relatively short space of time. While he looked super lean playing a frat boy in Bad Neighbours, he's a lot bigger for his next role in DJ flick, We Are Your Friends. As he steadily builds a more discerning fanbase, expect Efron to be running away from explosions on an IMAX screen near you soon.

Chris Pratt - 36

The star of Jurassic World and Guardians of the Galaxy proves that it's never too late to start eating clean and training hard, as his recent transformation has seen him turn from lovable goofball on Parks and Recreation to one of Hollywood's most bankable A-list stars, six pack and all. 

Pic via Chris Pratt/Instagram

After dropping about 60lbs, Chris Pratt is now in the best shape of his life at age 36, and credits it mostly to having given up beer for a couple of months, and he went from being the average guy to being in super hero shape, proving that it can be done with enough hard work and dedicatilon. Pratt also features as the cover star on July's issue of Men's Health, where he notes that he didn't just get in shape, he changed a lot of aspects of his life as a result: "getting physically sharp helps me get ready for other things in my life" 

Guy Pearce - 47

Australian actor Guy Pearce is one of those guys with leading man looks, who nonetheless gravitated towards more character-driven fare. Not afraid to drastically change his body shape for a role, he does just that for the part of a fitness instructor in upcoming indie flick, Results. Looking every inch the jacked, high end CrossFit fanatic he plays, Pearce was able to put on some serious muscle at an age when most men, even ones with past athletic prowess, are finding it difficult to stay in good shape. Firmly middle-aged, the talented thespian is physical proof that age ain't nothing but a number.

Brad Pitt - 51

To this day, most personal trainers are sick of being asked by clients how they can look like Brad Pitt in Fight Club, but even years on from that role, Pitt is still in incredible shape. Most recently, we saw in Fury that he's still got an enviable physique, and at 51-years-old, that is no mean feat. Pitt's routine included about two and a half hours of working out every day, as well as seven meals that were high in protein to fuel his intense sessions in the gym, He did allow himself the odd McFlurry when he felt the craving, apparently. The results were amazing, and proves that even after hitting 50, Brad is still much better looking than us...and has great hair.

Arnold Schwarzenegger - 67

Despite being probably one of the busiest men around, Arnold Scwarzenegger has never given up being ridiculously fit, as evidenced by his appearance in Terminator Genisys. He stated that he wanted to work hard to get as close as he could to the shape he was in back in the original in 1984, which meant packing on about 10lbs of extra muscle. 

Speaking to People magazine about upping the intensity of his workout again, he said that since he's always been in pretty good shape, it was like "riding a bicycle. You don't lose it. You don't forget." His routine consisted of getting a few more protein shakes in than normal (he does have his own line of gear with MusclePharm, after all) and two training sessions in a day, one cardio and one for weight training. At 67-years-old, Arnie still has the guns of a killer robot sent from the future, which makes us feel incredibly bad that we skipped the gym this morning.