How can I calculate and check for age?

Hi to everybody,
I never used Javascript but I think I will need it here.
Briefly, I'm going to ask in a survey the date of the test and the birthday and then what I would like to do is:
* calculate the age in years, month and day at the date of the test;
* check if the age is between age1 and age2 as needed;
* put a warning that says that the person should be between age1 and age2.

Is it possible?