It seems as though you are already doing quite well IMHO.
I got "the talk" on 4th of July when I was 19 from my father who happened to be hammered and told me "don't be a fool, wrap it!" before my brother and I had to carry him inside.
As far as your son being comfortable enough not to find it amusing and being mature about it so far...that's good. He'll take it seriously. However...he sounds like he's intelligent. Given how I was, when I finally decided the fun involved was worth the risk, I dove in headfirst. I was educated, and knew what I wanted, and how to get it. If your son happens to be in a similar mindset, you may be dealing with him being active around you if you make him feel comfortable with doing so at home. Keep that in mind. I avoided dealing with it until after high school for my own reasons. Afterwards...well, I didn't do much else. I'm not sure how you may take something of the sort occuring before your son is an adult and living on his own if that takes place.