The law.
However the age does vary between Provinces. Eighteen is the age of majority in: Ontario, Alberta, Manitoba, Saskatchewan, PEI, and Québec. The age of majority is 19 in: B.C., New Brunswick, Newfoundland and Labrador, Nova Scotia, the Northwest Territories, Nunavut, and the Yukon Territory. As in all matters I certainly wouldn't make legal decisions based on TERB, there may be apropos case law in Ontario.
As a minor your parents have legal control and legal responsibility over and for you unless you have been declared an emancipated minor by a court of competent jurisdiction.