Aging Characters wioth Variables Options

[Geekman]

Can I make a variable go up everytime another variable has a certain constant?
i.e. Variable 1 has 3 as the constant. Everytime Variable 2 has a certain number as it's constant, Variable 3 raises by 1.
This could be used to make a character age, with 1 being his birthday, 2 being the number of days that have gone by, and 3 being the character's age.
If you can find another way to make a character age, please comment.