I was booking train tickets from Rome to Venice on Trenitalia app. We are a family of 4, with a 15 yrs old (currently 14, but will turn to 15 yrs old at the time of travel) and 9 yrs old. When searching tickets, I put 3 adults and 1 child, because the older one will be 15 years old at the time of travel. I select FrecciaFamily, so the 9 year old would be free. I entered birthday in the app. However, when making payment, the app recalculated the price and changed the 15 yr old from adult to child, and thus free. I double checked birthday is correct. I also tried a few different travel dates. The then-15 years old is consistently counted as a child for ticket.
I am confused, so I searched Trenitalia website. The language is “ la gratuità del viaggio per i ragazzi fino a 15 anni (non compiuti)”. Google translate “ free travel for children up to 15 years of age (not yet completed)”. Does that mean 15 years old is considered child and travels free? Do want to get in any trouble on the train.