The minor who turns 18 after entering Italy is entitled to have an extension first of his family permit. After that, he will need to secure his or her own visa (he can obtain a study permit or a work permit if he finds a job).
How could dependents keep status in the Italian Residence by Investment program when they age out?
I want to apply for the Italian Residence by Investment program and invest 2 million euros in government bonds. My son is currently 17 years old. When he reaches 18 years old, does he have to invest in the program of his own again to keep his status?
The investor is entitled to bring his underage children and the adult ones with him into Italy, as long as they are economically dependent on him/her (meaning they're still unable to provide for themselves) for the entire duration of the visa. When the visa is about to expire, the adult children may apply for a study or work permit of stay just in case he/she would like to remain in the country.