A childhood belief about getting older

When i was little, i used to believe in old peple were crazy because their brain as old too and they lost their mind so i scared about old people.
When i was little my great-grandmother lived in a pension house and every week with my father and my grandmother we went to vistit her . The day of her birthday we brought a big cake so i put it in the kitchen of the pension house, and during the party a grandfather ate completely my great-grandmother cake, so she diddn't have a cake for her birthday and i was very scared of this grandfather because i thought he would eat me too