When can my sophomore son take a practice PSAT?

he is in honors algebra 2 if that is important. id like him to do it soon for a variety of reasons but i’m not sure if the math is all there.

Collegeboard has practice tests you can download. PSAT/NMSQT Full-Length Practice Tests - SAT Suite

Also Khan Academy has practice tests
https://www.khanacademy.org/test-prep/sat/new-sat-tips-planning/new-sat-how-to-prep/a/full-length-psat-nmsqt