The pleasures of trekking in the world's highest mountain ranges cannot be overlooked. Neither can the dangers. Altitude sickness can strike some people at as low as 8,000 feet, but serious symptoms do not usually occur until over 12,000 feet. Even then it is not the height that is important, rather the speed in which you ascended to that altitude.
Acute mountain sickness (AMS) is actually more common in fit young men because they are more likely to attempt a rapid climb by racing up the mountain like some ego boosted super hero! As a general rule, it is far safer (and more enjoyable) to avoid altitude sickness by planning a sensible itinerary that allows for gradual acclimatisation to high altitude as you ascend, (You can race back down as fast as you like!).
What is High Altitude?
It is difficult to determine who may be affected by altitude sickness since there is no specific factor such as age, sex, or physical condition that correlate with susceptibility. Some people get it and some don’t.
Most people can ascend up to 2,500 metres (8,000 feet) with little or no effect. If you have been at that altitude before, you can probably return to that altitude without problems as long as you are properly acclimatised. If you haven't been to high altitude before, you should exercise extreme caution while doing so.