@Thingsthatgo I teach a related subject at Oxbridge. Don’t worry about not being an “Oxbridge family” - that kind of thing doesn’t matter. Nor do you need to worry yet about extra courses and taster days and outreach stuff and so on — that will all come much later, from 16/year 11 onwards. We also don’t care about extracurricular activities and hobbies, so don’t worry about that either.
The main thing your DS needs to be doing is to READ. It doesn’t even really matter what: a wide range of things that interest him and are around the subject he likes (and related subjects): popular history, broadsheet newspapers, current affairs, a bit of proper classic literature, some history of medicine, science or philosophy, non-fiction — everything that interests him is good. The thing is go beyond narrow subject confines and get him reading across disciplines and thinking about broader issues — not just “history”, but all sorts of things about how and why people think what they do. He might enjoy some introduction to historical method or historiography (start with an oldie but a still-good introduction: EH Carr’s What Is History?, and go from there).
Watch the news, Panorama, documentaries about important events, listen to discussions on Radio 4 and programmes like In Our Time. Some classic history series by people like Simon Schama. Talk to him about politics, recent history, international affairs, what he thinks about big issues. Debate different points of view. Talk about your experiences of historical moments in your own life (what it was like to experience 9/11, the Millennium, the fall of the Berlin Wall, Obama being elected, etc. etc.)
And, though at Oxbridge we don’t take any notice of extracurriculars and so on, what IS super useful and helpful is if you can get into trips to museums, looking at things like historical and archaeological sites, and so on — doesn’t have to be huge amounts or expensive, we’re lucky in this country that there are plenty of them and plenty of free museums around the place. See some theatre, go to art galleries. You may be doing all of this already, in which case, great! The idea is not to look “cultured”, but to get him cross-comparing a range of different kinds of historical and social experiences and thinking about how they broaden his knowledge of the disciplines he enjoys. Get him thinking about big questions like: what effects does museum curation - how you display objects - have on how we think about history? What kinds of relationships are there between history and literature? What kinds of ways do we think about very recent history - eg. within our lifetimes - that are different from how we think about “older” historical periods? What’s the difference between current affairs and history? Is there a philosophy of history? Is archaeology history, or something else?
There are no “right and wrong” answers to these kinds of questions, but just thinking and reading abut them and debating them is getting towards the kind of thinking that prepares you for an Oxbridge degree (and higher education in general). None of this has to be expensive, and you certainly don’t need to pay for courses or tutoring or preparation of any kind. Free museums, the library, iPlayer and so on are great resources. It’s all more about getting into a habit of mind than anything else. Also, it will tell you and him if he enjoys this kind of thinking and intellectual debate: it’s above all absolutely essential to be passionate and engaged with your subject, and to really love the learning process.
Good luck to you and your DS, OP; and enjoy!