I know some, not many, smart 20 year olds who could easily manage an entire fast food restaurant after a short couple months of training.
When I worked in that industry most of the asst managers were late teens early 20.. if they did well could be tapped to be a store manager after a few years.
Weren’t the majority being tapped to manage a store at that age,, but they did exist and that was nearly 40 years ago