The Foundation Level exam (CTFL) has no pre-requisites. Sufficient Preparation on the syllabus topics (obtained either through attending a course provided by an accredited Training Provider, from professional experience, and/or through self-study) is recommended. To take the Advanced Level exams, the Foundation exam must have been successfully passed.
The possession of the Foundation Level Certificate may have to be proved. ISTQB® also recommends practical experience before taking this exam. In addition, sufficient experience is required, so a JOSTQB representative may call you for a quick evaluation. The required experience is usually three years, but it depends on each exam.