At over which level in mmol for fasting glucose should diabetes meds b started if diet and lifestyle changes hav been made?

Depends. Diagnosis of diabetes is made if two fasting blood sugar values are higher than 7 mmol. However, it is some times prudent to start medication in a person with pre-diabets. It would require and individual evaluation, best done by your doctor. For information on pre-diabetes, you may consult this site.