What can cause the presence of protein in urine at the age of 17?

Many possibilities : Needs to be explored. Could be from exercise, supplements, infection, kidney problems. If you exercise a lot or use supplements, stop for a week and recheck.

Rule out orthostatic: Many healthy young people have so called orthostatic proteinuria, i.e. Present when they are up & about but not at night when recumbent. It is benign. Mt bladder 2 hours after lying down, then have first voided am urine tested. Trace protein when found is usually benign. However true proteinuria, after excluding above would need to be evaluated by nephrologist to rule out kidney disease. Good luck.