Re: Olympiads
1. Not very - everyone at my school does the Maths Olympiads. As for Physics Olympiads - never knew there was such thing, but I suppose this is the first year we've done Physics so who knows?
2. We did Maths Olympiad since Year 7. Personally, I did it from Year 5, all the way up until now.
3. It's never to late to try. If your school offers it, I would definitely recommend doing it. If not, talk to your Maths teacher, or Head of Maths, and see if there are any 'enrichment' programs running at your school. I think the Year 9 Maths Olympiad course is known as Noether (correct me if I'm wrong). As for Physics - talk to your Head of Science, or Science teacher - however, don't be too disappointed if you're not allowed to do Physics Olympiad - you're only in Year 9.
4. I have no idea - I'm not -that- good at Maths.
5. If you're referring to National/International, then probably? I dunno. As for the school one, just your basic Grade maths will do.