Starting in Year 10 means you have plenty of time! I attended this year and the last, and I started learning CP properly later than that (you can see my blog post if you want to know more). The best way to prepare (in my opinion) is first, to have a good foundation in general programming and CP, then once you're confident you should definitely do all of the past paper questions; the format of the BIO is very different from other national informatics olympiads.

Also, you can join our Informatics Olympiad server, where there's a lot more finalists you can talk to! Add me on discord -- myst06 -- and I can send you an invite :)