I was amazed myself.
I Googled the phrase "Your age by diner & Restaurant Math," and found other blogs featuring this game (the first link that popped up is http://mathplay.blogspot.com/2007/04/your-age-by-diner-restaurant-math.html). Blogger Praveen Puri also gives an explanation on how the process works.
But before you go to Mr. Puri's site, take time to enjoy the mystery first by grabbing a pen, paper and calculator (I used Windows's in the accessories menu) and go through the process.
The email advises us to scroll down only after completing the steps.
"It takes less than a minute. Work this out as you read. Be sure you don't read the bottom until you've worked it out! This is not one of those waste of time things, it's fun," the forwarded email said.
YOUR AGE BY DINER & RESTAURANT MATH
Step 1. First of all, pick the number of times a week that you would like to go out to eat. (more than once but less than 10)
Step 2. Multiply this number by 2 (just to be bold!).
Step 3. Add 5
Step 4. Multiply it by 50 (get the calculator out)
Step 5. If you have already had your birthday this year, add 1759. If you haven't, add 1758.
Step 6. Now subtract the four digit year e.g., 1970, that you were born.
You should have a three digit number.
The first digit of this was your original number, or the times you want to go out to restaurants in a week.
The next two numbers are YOUR AGE!