Quite simple actually, it was found because you gave it your date of birth. Just use variables instead of numbers:

let’s say the original numbers is a
then we multiply it by 2: 2a
add 5: 2a 5
multiply by 50: 50(2a 5)=100a 250
add 1756 (or 1757, if you already aged by one this year, so it’ll balance): 100a 2006
then you reduce your year of birth from it, which simply reduces your year of birth from the current year: 100a (2006-b)
so your original number is still there but multiplied by 100, and the rest is your age.
It won’t work next year (unless you add one more), and it won’t work if you are over 100 years old.

Poke .. I am impressed … and sad about my not existing smartness