To not eat after 7 pm is a common tip among people who wants to lose weight.
But I don't think it only applies to those. Even those who has normal weight should go after this rule too in order to stay fit
It's after 7 pm the metabolism is at its lowest, which means it's harder for the body to burn the calories you eat at these hours. If you do need to eat at night, make a fruit salad or something likely.