Hi the BPS (British Psychological Society) have lectures once a year designed for A level and undergrad students, I think it's called psychology4students, the BPS also has a student section which has a one day conference once a year it's worth signing up with them.
People like the RSA, Royal Institute and Intelligence Squared all have really good public talks, not all psychology based but check out the websites.
Once you start your degree you will be expected to read journals in the different areas so you could have a flick through them, don't worry if you don't understand them all! I would also recommend buying Andy Fields statistics book and getting a head start on that as that's the bit most people find the hardest!
Good luck and enjoy!
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