Are there some process of law to delay the age?

I know sounds stupid,but I come to Canada and I am 20 years old I was born in Canada,but all my life i was in el Salvador now i come back to Canada.99% of the people told me you have 16 years!! also I'm high school easily i look like a teenager,my question is can i delay my age to 18 years old?? because is awful that you have 20 and the people confused with teens of 16 or 17 years,also my mind is not a 20 years old...sometimes i think........really i have 20 years??? what's your advice