How can my minor son keep his status in Italy when he turns 18?

I was told that if I obtain an elective residence visa of Italy, my 16-year-old son will be able to join me by applying for a family visa. How long is this visa valid for? Does he lose his eligibility to live in Italy when he turns 18?

Answers

On Alessia Ajelli answered:

When he turns 18, he will be able to renew his family permit for the same duration as yours if he remains financially dependent on you.

On Marco Mazzeschi answered:

When he turns 18, he will be able to renew his family permit for the same duration as yours if he remains financially dependent on you.