Agree. Be glad he is asking you and don't refuse to answer anything at all*. I would also add that I have taken several opportunities to point out that what they see in online p orn (which of course they all deny watching) is not a true reflection of most people's s exual experiences, that women are often coerced into taking part in these things and are being exploited, and that issues of consent are never reflected in them. I think it is very important that both boys and girls are aware of the pressures on women to groom their bodies in certain ways - for me this is something I wanted mine to know was unacceptable and I don't want my sons contributing to that pressure or my daughter feeling she has to succumb to that culture. I also think it is hugely important to teach both genders to be able to say 'no' at any point but to respect the feelings of others too. One of the things which seems to have gained popularity is girls performing a particular act on (sometimes several) male friends at parties - personally I think that needs challenging on both sides, though others seem to think it's ok and at least the girl won't get pregnant. Apparently girls think it is a compliment to be asked
. For me all those issues are more central to this than the technicalities, which are pretty mundane when you reduce them to mere facts.
Soon he will know more than you anyway, so take the chance to open the dialogue now, even if it is uncomfortable.
* though I think questions about what you have done or do do are probably off-limits in the same way as you won't expect to be asking them in huge detail exactly what they choose to do when the time comes.