Simplifying a lot, once you age, your cells have accumulated lots of genetic and epigenetic defects, so they are more likely to become cancerous if you let them

Simplifying a lot, once you age, your cells have accumulated lots of genetic and epigenetic defects, so they are more likely to become cancerous if you let them divide quickly. Besides, you have less lymphocytes looking for carcinogenic cells, as your immune system is older.