If you build Date objects for current time and birth date, you can work out the time between them with pretty simple math. Look at the doc for Date ... do you see a method that returns a number we might do math on? See if you can compute age in days or years. Avoid months - they're all different sizes which makes them mostly meaningless.
These are pretty vague hints ... I hope you have fun digging out the details yourself.
A good question is never answered. It is not a bolt to be tightened into place but a seed to be planted and to bear more seed toward the hope of greening the landscape of the idea. John Ciardi