LONDON - It's time, the judge said, for Jeremy Walzack to "grow up."

The 22-year-old London man, with rings on almost every finger, studs in his ears and dressed in a white hoodie and matching nylon pants, listened from the prisoner's box.

"You are going to have to grow up, you have to control your impulsivity, you have to deal with your bravado," Superior Court Justice Helen Rady said.

Moments earlier, Walzack had to reach into his pocket to turn off his iPod. His cellphone had gone off earlier during court.

The young man, who portrayed himself as a wannabe gang member and a hood, was dealt a hard lesson when he was sent to jail for a mandatory year yesterday for what the Crown described as a "cowardly" act.

A jury found Walzack guilty in November of assault with a weapon and use of an imitation firearm while uttering threats for an attack in Vauxhall Park on Aug. 27, 2007.

The firearm conviction carries a minimum one-year sentence.

Walzack sprayed bear spray into the eyes of Rocky Hernandez, 14, and shot off a starter's pistol. No one was injured.

Walzack claimed he was acting in self-defence because Hernandez tried to rob him of jewelry. Hernandez said he was injured during an argument between the friends he was hanging with and Walzack.

Walzack's lawyer, Richard Braiden, said during his sentencing argument his client suffers from attention deficit-hyperactivity disorder and often acts impulsively. He has been involved in a committed relationship recently that has helped him sort out some of his behavioural issues, he said.

Braiden said Walzack's crime was not worth a year in jail and called the sentence "harsh and excessive." The imitation gun, Braiden said, was "extremely small" and witnesses thought it was a cap gun or a toy gun.

But he acknowledged Rady had no choice.

Assistant Crown attorney James Spangenberg said Parliament acted to harden sentences for gun crime because "guns and gangs are a serious problem."

"In sleepy old London, guns are becoming more common," he said.