What are stomach cancer incidence per age group paticularly in the 20s age group?

Quite low.: There are likely no figures per age group on stomach cancer unless you look at a site like the american cancer institute/society or cancer treatment centers of america which may have this. However, it can be said that this is quite low in incidence in the 20's. This disease usually presents at age 55 or older, since it takes decades of exposure to develop. Avoid smoked foods and eat more fiber.

None at your age: Extremely rare things happen very rarely. Most gastric cancer occurs after age 60. Please see a doctor to review your risks and answer your questions that you have asked here repeatedly.