You will need a calculator for this trick.
1. Pick a number between 1-10.
2. Multiply by 2.
3. Add 5
4. Multiply by 50.
5. If you already had your bday this year, add 1762.
6. If you haven't, then add 1761.
7. Subtract your answer from the 4-digit year you were born in.
8. The first digit was the number you picked at the start. The next digits are your age.
I bet I know your age! =)

Comment if it worked!. If it didn't then you did the calculations wrong.