Age
Although cancer may occur at any age, the average age for cancer diagnosis is between 65 and 74, depending on the type. Over the years, you have been more exposed to carcinogens and inflammatory processes, and there has been more time for symptomatic slow-growing cancers. In fact, the body becomes less effective in identifying and killing cancerous and precancerous cells.
That said, there are some more common forms of cancer in children, including bone cancer and some types of leukemia.