Nice segue from the marriage topic, I had nothing to add to that other than my thoughts about how important commitment is to any marriage no matter the age. 
So now, onto the sex. It has been important for me to impart on both my son and daughter about self respect, self control and respect for others as it pertains to sexuality. I talk to them fairly often about many aspects of sex, the primary goal being it is an activity to be mutually enjoyed when they are in a caring, loving relationship. I tell my gal she never need to succumb to the pressure of 'giving it up' - I have gone as far as talking to her about taking care of her own 'needs'. I tell my son that he never should pressure a girl to 'get it'
I tell them both about the beauty of a sexual relationship within a committed loving marriage/relationship. I tell them too, that sex changes over time.