I don t understand why the "total_age" is still 0. It looks like that for is not working

With Python, indentation matters. Trying to decide what your code may or may not do without the original formatting preserved would prove nothing more than a guessing game. See How do I format code in my posts?
Please post a reply that includes your code with its formatting preserved, and someone should be able to help you.
Posting a link to the exercise would also be very helpful.