At what grade or age are we required to take the PSAT and SAT exams?

In the UK SAT exams are taken at the end of each Key Stage. You get the vital ones when you are 10/11 (Year 6/5th Grade), and then again when you are 13/14 (Year 9/8th Grade). If it's the same in USA, or wherever you are, hope this helped. :)