Age is just a number.
That's what they say, right?
Well, it may be just a number, but as that number creeps higher, humans tend to get weaker, less explosive and more prone to injury.
That's why most professional athletes tend to be in their 20s, a period when the body's capability for things like strength and endurance naturally peak.
The average NFL player, for example, is 26.6 years old.
Meanwhile, the average NBA player is 26.8 years old.
The MLB skews a bit older, but the average player is still just 29.2 years old.
However, a number of athletes have defied Father Time to continue playing professionally long after their peers have retired.
These are the 21 oldest professional athletes still playing in 2018.
Photo Credit: Wikimedia Commons, Lachlan Cunningham/Getty Images, Icon Sportswire/Getty Images