If it's something you id that is well recognised such as a grade at a musical instrument, a professional qualification ie red cross first aid certificate, DoE or some other instantly recognisable scheme by all means put it on. Otherwise avoid going too far back.
Remember only include things that add value to your CV, put yourself in the shoes of the person reading it, will they be interested, will they even know what it is?
Keeping it down to one page is also a good guide. It will impress far more, it will be far more succinct, and if you've managed to edit it down to such a length you can be pretty sure what you've included will add value.
One of my friends at Oxford showed me his CV and you wouldnt believe the impact a one page CV where everything add's value can have on the person reading it. Just because you can make it longer does not mean you should. If you add a second page will they even take the time to read it properly? Probably not!