Anyone can develop altitude sickness, no matter how fit, young or healthy you are. In fact, if you’re physically active while at a high elevation, you’re more likely to develop it.
Chances to get altitude sickness depends on a few things: how quickly you move to a higher elevation, how high up you’re going, the altitude where you sleep/rest, etc.
Your risk also depends on where you live, the altitude you’re accustomed to, your age (young people are more likely to get it) and whether you’ve had altitude sickness before.
Some research suggests our genes can play a role in the body’s ability to handle higher elevations.