POMIGLIANO D’ARCO, Italy — After leading the anti-establishment Five Star Movement to a stunning result in Italy’s national elections, Luigi Di Maio returned triumphantly to his small hometown near Naples.

Thousands of adoring supporters chanted “Pres-i-dent” and “Lu-i-gi” and gave their local boy a bouquet of yellow flowers. But no one was more ecstatic at his success than his mother, Paola Esposito, who said she was “very, very proud.”

And to think, she added, he was living at home “until five years ago.”

Now Mr. Di Maio, 31, a college dropout and former soccer stadium usher, may be first in line to become Italy’s next prime minister after the Five Star Movement won the most votes in the March 4 election.

His improbable ascent is a measure of Italy’s suddenly turbulent politics. But it also reflects the youthful, new-kid-on-the-block appeal of the Five Star Movement, as well as what critics say is one of its most glaring shortcomings — a lack of real-world experience.