Okay, in response to Candela, there are two different opinions going on this argument. One person is obviously religious, and one is not.
Both of your responses are right. If you believe that sexual intercourse is bad, then by all means it is.
If you believe that it isn't bad, then fine.
Everyone has a different perspective on things. A psychotic pedophile's idea of what's right wrong is extremely different than a Bishop of a church. Of course, the pedophile's idea of right will most likely conflict with the law, which, unless you like jail, means you can't do it without external consequences.
In my experience, the social norm sees sexual intercourse during teenager years a very "normal" thing. Is this right or wrong? Depends on what your beliefs are.
However, on a physical evidence basis, you must admit that sexual intercourse is not wrong, and if anything, can be very stress relieving and helps an individual enjoy life. If you take things on a religious basis, then this is obviously different.
You're both right.