Percentage wise what are my odds of stomach cancer at age 22?

Very low- unless..: The incidence of stomach cancer at age of 22 is very rare. You should not worry about this. If multiple family members had stomach cancer, especially at younger age ( less than 40) -then that would be a different scenario. Your risk to get other problems like depression, getting involved in motor vehicle accident , infection is way way higher. Please go and talk to your primary doctor in detail.