The unnamed man was stopped at Turin Airport wearing a pilot's uniform and using forged ID cards, police said.
He was charged with endangering air transport security and impersonation.
The suspect led police to a garage containing neatly pressed white shirts with epaulets, black trousers and jackets, like those worn by pilots.
No motive for the man's actions was reported immediately.
Police have established he sat as "third pilot" in the cockpit of an Air Dolomiti plane which flew from Munich to Turin in April. He did not touch the controls, however.
Air Dolomiti is part of the German airline Lufthansa, which gave no details when approached by the Associated Press news agency but insisted he could not have boarded the plane without a ticket.
Investigators are now trying to establish if the man flew on other planes.
Police had long been investigating the suspect, who had allegedly created a fake identity as a Lufthansa pilot named Andrea Sirlo, complete with a Facebook page which included fake flight attendant friends.
They said they had been alerted several months ago after he introduced himself as a captain to a civil aviation lieutenant, who became suspicious because he seemed too young for the job.
Police tracked him down from photos on his Facebook profile, in which he is apparently shown posing in uniform and sunglasses in front of planes.
Officers approached him in a bar outside Turin Airport's check-in area, dressed in a pilot's uniform with no company logo on it, and sipping coffee.
In the garage, officers also found fake IDs and fake flight theory manuals, the Italian news agency Ansa reports.
"On at least one occasion in 2012, pretending to be a pilot of a foreign commercial airline, and with a fake name, he succeeded in flying as the third pilot in the cockpit," police said in a statement.
According to Ansa, a flight took place on 6 April.
In addition, a profile on a website where users can track their flights also shows a "Pilot Andrea Sirlo" flying from Munich Airport to Turin on 23 October last year.
The case has echoes of the 2002 Hollywood film Catch Me If You Can, in which Leonardo Di Caprio played Frank Abagnale, a real-life con-man who flew as a fake Pan American pilot in the 1960s.
Sirlo is the name of a flight corridor over Turin.
Police in Italy have arrested a jobless man who posed as an airline pilot, tricking his way into riding in the cockpit of at least one jet.