I saw your post on the other thread, ageing and I'm so glad you started this one. My DS is also 8 and I've realised that it's getting to the stage where I need to start talking more about the specifics with him. I hope I've already been laying the groundwork - your body is your own, you get to say who looks at it or touches it, the same goes for other people's - they get to say who looks/touches their body. And rough and tumble has to be something everyone's enjoying - if someone says stop, you stop. That applies to tickling, play fighting etc.
But I've noticed that kids his age do mimic the sexualised behaviour of adults and older siblings - twerking, hip thrusting, etc. So I had to sit him down the other day and try to find an age appropriate way of explaining why this wasn't right - that for instance, hip thrusting in grown ups towards someone just quietly minding their own business was often the start of more and worse unwanted behaviour, which is why you shouldn't copy that behaviour, even as a joke.
Argh. I wanted him to have a few more years of childhood. But sooner or later, someone's elder sibling's going to show them porn on a smart phone, then they'll all start looking out of curiosity, and I have to pre-empt that so he knows that crap is nasty and bears no resemblance to proper, consensual, mutually enjoyable relationships between adults. All without introducing age-inappropriate stuff myself. I don't want him psychologically damaged by this crap. I don't want him buying into the misogynistic crap fest that is available a few swipes away on a smart phone.
He is pretty good at spotting sexism, though. And very caring towards others. I have to just pray that those are the foundations I can build on to get him through the next 8 years safely.