The only certification that is required is the full CompTIA A+. Back when I took it, this was split into two different tests: one for hardware, and one for software. This may have changed since then -- it would be a good idea to check what exams you need to complete to get full A+ certification.
The only other requirement is that you must be at least 18 years of age. People tend to keep 'interesting things' on their computers that should not be exposed to minors.
Once you're fully A+ certified and meet the age requirement, fill out an application for a job in computer services, and away you go!
