late period

I've had my period for about 4 years now and for about 2-2.5 years it's always been perfectly on time or never more that a day either late or early. Only a few exceptions to that when I synced with my friend and was 9 days late but I know I'm not late because the only girls I hang out with r synced and just got off theirs. I'm not sexually active so it's not like I can be pregnant so is there a point where it becomes concerning if after 4 years I just stop getting it