Am I eligible?

I'm a beginner. The issue is that my D.O.B is 19th Dec 1989 and by 1st January 2011 I'll be 21 years old. What I need to ask is that will I be eligible for appearing in 2011 ? I'm confused regarding this age issue as I've heard that D.O.B is counted from March to March and if counted like that I guess I'm not eligible to appear in 2011 but 2012.