Opinion on a four year age gap?

I am almost 17 and he is over 18. Don't worry I'm not even with him, but I am very curious about other people's opinion on age gaps. I see no problem with it for the most part, but I want to know what you all have to say. And yes, I do understand that an adult/minor relationship is not legal (again I am not with him I just want to know what everyone thinks).