wow hello! you are very ahead of the game!can i ask what you want to study at uni? that might give me a better way of answering this question.honestly, i dont think its a good idea to start you personal statement now. Im in year 13 (so S6 in scotland) , having sent off my application to oxford and also gotten interviews from oxford for maths, and i began my ps in August before y13.in terms of writing the ps itself, you dont have to be absolutely cramming it with activities you have taken part in. for instance, i wrote about a couple of books i read surrounding mathematics, so id recommend you do the same for your subject. i also did a team project about AI, which i linked back to maths in my own way. i wrote about UKMT maths challenges, and about a lecture i attended, which sparked me to research higher level maths on my own.then other things i wrote about were work experience which i did in a hospital, being head student and getting an ILM award, and my hobbies like art and reading.in my case, i had a sort of running theme in my entire personal statement, which was linking unconventional things to mathematics in some way. the most important thing in my eyes is linking everyyyything back to your subject in some way, OR making sure you detail what you have learnt from it. this doesnt have to be very direct, but it could be implicit as well.if you'd like to, you could tell me some of the stuff you have done, and I could help you with choosing what you should include and what you might want to leave out? 🙂