From your own link:
Buttigieg joined the Navy Reserve in 2009, when he was 27, as an intelligence officer through the Reserve's direct commission program offered to applicants with academic degrees. It made him an officer without first having to go through the months of officer training, as most did.
He did have to go through basic training, however, and he told ABC News he got the full experience: being woken up in the middle of the night on the first night, superiors inspecting the rooms for the slightest infractions.