Seventh grade is FAR too late to have sex ed. It should be done in elementary school. By the time I was in the eighth grade, several of my classmates already had children.
By the time I was in tenth grade, I knew very few virgins.
By the time I graduated high school, nobody I knew had not engaged in some form of sexual activity, and I personally consider it weird if someone has not been sexual by the time they leave high school.
I think that teens should begin experimenting sexually at 14, or when they enter high school. I think it is important to their development, and helps build confidence. It can be incredibly awkward for a virgin to enter college when all their classmates have had sex or had some form of physical or oral sex. I think it is important to grow sexually, especially after puberty when nature intends us to.
I think it is important to teach sexual education at a young age, say, fifth grade because it is important for people to understand sex well before they do it. Teens need to know that sex is okay to do, and need to know all the risks and protection styles that come with it.