How long does marijuana stay in system if your not a frequent user?

Depends on the definition of use. Also on the method of detection.

On a MedTox drug screening test the detectable level of THC for a preliminary positive result is 50 ng/mL. This is the recommended level by the FDA. *All preliminary results must be confirmed by GC/MS (mass-spec) before anything is admissible in court or may be used to defer employment.

If you are tested with a GC/MS any amount greater than 15 ng/mL will be seen as a positive test and can be used as evidence against you.

A 50 ng/mL level can be detected 1-7 days after a single use and up to 30 days in chronic users. The rate of elimination is also affected by a person's body chemistry and composition.