The short answer: 16 years old on the Nepal side, 18 on the Tibetan (Chinese) side. But the full picture is more nuanced—and far more demanding than a birth certificate suggests.
Nepal (South Col route): The Department of Tourism sets the minimum age at 16. There is no upper age limit, though climbers over 75 face additional medical scrutiny.
Tibet/China (North Col route): The Chinese Mountaineering Association requires climbers to be at least 18 and no older than 60.
Despite the legal minimums, the typical Everest climber is in their 30s or 40s. The reasons are practical:
Jordan Romero (USA) summited at 13 in 2010—from the Tibetan side, before China tightened its age limit. Ming Kipa Sherpa (Nepal) summited at 15 in 2003. Both sparked ethical debates about parental consent, commercial pressure, and child endangerment in extreme environments.
If you're 16 (or 18) with the experience, fitness, funding, and a reputable operator, you can legally climb Everest. Whether you should is a question only honest self-assessment—and perhaps a few more years on other peaks—can answer.