I'm really wondering what is the legal age to go into a relationship with for a 16 year old?

Back at school, in health class, I was told that you can not date anyone more than 3 years older than u... if you date anyone more than 3 years older than u.. The person would go to jail for it. But I'm still not sure.

I'm 16 years old... and I wonder if it would be legal if I were to have a boyfriend that is 20 years old. (that would be a 4 year difference). But to be real honest, I really love this guy. And he really respects me. My opinion on age difference is that... as long as we love each other.. there shouldn't be any problems...

So... is it legal?