can any body tell me how can we calculate our age?

There was a Lot of confusion in This for me.But, My parents say It should be Calculated Like if you are born On January 2000.then,asof today you are 6 years & on the next month after your birth day it will be said as you are 7 years old. Its not only confusion with people but with websites also. I have signed up in many websites some have calculated my age as 21 & some as 21. I am little confused about it. I believe i am 22 now. i was born In december 1984

in general terms or we can say lawful or official terms age is calculated excluded the birth year....for example if somebody birth on year 1987..so 1987 is excluded and from 1988 to 2006 is calculated...