To solve this question we have to make deduct these 2 years. 2021 minus 2015 will give the answer.
You are 6 years old.
(72 months are passed.)
From 2015 to 2021 there are 6 years. If you want to learn your age in 2021 (born in 2015) your age is 6.
Let's see what will be your age if you born +1 or -1 from that date.