Found this on an online game a play it's fun and worked for me

Don't tell me your age - it probably wouldn't be the truth anyway - but the Cadbury Man will know!
YOUR AGE BY CHOCOLATE MATH

This is pretty neat.
DON'T CHEAT BY SCROLLING DOWN FIRST!
It takes less than a minute..
Work this out as you read.
Be sure you don't look at the bottom until you've worked it out!
This is not one of those waste of time things, it's fun.

1. First of all, pick the number of times a week that you would like to have chocolate (more than once but less than 10).

2. Multiply this number by 2 (just to be bold).

3. Add 5.

4. Multiply it by 50 (I'll wait while you get the calculator).

5. If you have already had your birthday this year add 1759...if you haven't, add 1758.

6. Now subtract the four-digit year that you were born.

You should have a three-digit number.

The first digit of this was the original number of times you want to have chocolate each week..
The next two numbers are
YOUR AGE! (Oh YES, it is!!!!!)
THIS IS THE ONLY YEAR (2009) IT WILL EVER WORK, SO SPREAD IT AROUND WHILE IT LASTS!
Cadbury Man knows all!