Age Gap

Alright you guys I need your opinion about the notorious age gap. How do you feel about a 5 year age gap? For instance 16 with 21? I'm curious as to how people view the age gap issue. Most people I know are iffy about it but at the same time they say that life doesn't magically start when someone turns 18 because in your late teens (16-17) you're starting to venture out more and that in this day and age it's almost impossible to pretend that life only exists for teenagers in high school.