Last year my CV was 6 pages - although there was a fair amount of blank space on it as I thought it much neater to try and not break up a section by having it span across 2 pages. Also as I rule I figured that I need to impress the prospective employer with this single document, and one way of doing that might be to show that I'm capable of writing decent summaries. I now tend to leave that for the covering letter (which looks 100x better if you can fit it on a single page, IMO).
This year I decided to give it an overhaul and it's now on 3 pages. I tried to make it fit on 2 but that really wasn't letting me emphasise my qualifications, skills and experience in the way I wanted to. An agent who has seen both the old and new said it was better and more 'snappy', he actually asked if I'd got some professional help to review it which is probably a good sign
What I would advise for younger people is that once you start getting some proper work experience (relevant to the type of roles you are applying for), start cutting out some of the 'filler' that you've had sat on there for years, like GCSE results, activities you did at school/uni etc.
When I first knocked out my CV I had all my subjects and grades listed, because that was my strength (I figured row-upon-row of As looked impressive) and I didn't have any work experience. However by last year my CV had basically bloated up to 6 pages because I was adding more and more work related stuff, but not streamlining it and clearing out the old stuff no-one cares about.
edit: out of curiousity, those with a lot of experience/skills, what font size do you use to fit it on 2 pages?