make sure the important stuff is on page 1, if you have a hundred or a thousand CVs to look at you will make the initial decision whether to bin it or read without turning the page.
2 pages is ideal, but if you have 40 years of varied experience why not go a bit further. In academic work you might have to list papers etc which can run on. With computers you can adjust your CVs depending on the job so a CV that does not focus on the relevant is not good.
As far as GCSEs are concerned, if the job advert says you need 5 GCSEs then put them on page 1, if it says a PhD in nuclear physics they can slide to the end of page 2 as "5 o-levels including home economics and woodwork"
If you are 18 the secondary schooling is important, if you are 50 it's not.
I once read a CV of a 30 year old that mentioned a prize he won at primary school, you giggle before binning it...
I have received 20 page CVs, who wants to hire a guy still harking back to what he did in 1952?
Keep all the bull shitty stuff for the cover letter. This should tie the advert to the CV. If the ad says experience in sales and management and degree, then use the letter to say "as you will see in my CV I have been in sales with 3 companies rising from tea boy to general manger...etc. Don't go on about what an amazing self-starting problem solving team player you are