I think that the people around me consider me intelligent. I don’t think I have a truly natural skill or advantage that goes over and above anyone else, though. What I do have however, is tonnes of knowledge and experience. I read constantly. When I’m not reading, I’m listening to audiobooks or podcasts. For me the key to building a wider understanding of everything, is to mix up sources and types of information. With books, I read a rotating mixture of classics, informative, biographies, and fiction. It helps to then broaden your outlook overall, as you have this mesh of facts, viewpoints, other people’s experiences from across the world and time, with which to create your own opinions.
I would strongly recommend an online access course (you then don’t need A-levels for a degree), and learn how to learn. It’s a skill in itself, and the structure of academic learning is very good at teaching you how to form opinion, and how to lean on evidence and to gather information before putting your own potentially biased or ill-informed opinions out there.
Access the things that interest you, if you love looking at beautiful art, go to galleries near you. Travel whenever possible, and take in cultural activities at every opportunity. Again, every experience adds a layer of thinking and understanding to your mind. I had to meet someone recently, and chose a free public gallery instead of the coffee shop that was two minutes away. I’m not saying that makes me some kind of pillar of intelligence! The point is, that these little decisions and extra thought going into how you spend your time, where you go and who you interact with, can build you understanding and by extension your natural intelligence.