I’d always advise one a4 page if possible for entry level jobs, two pages for people who have a lot of experience, and an absolute maximum of four for high flying professionals. Mention in detail what you have done for the last 10 years, and just summarise anything prior to that. Anything more than 10 years old does not require immense detail unless it is completely relevant to the role you are applying for.
Keep it short and sweet, or else you risk boring your prospective employer!