STAMFORD - When the Alive@Five concert series kicks off in July, the only ones rocking to the beat in Columbus Park will be ages 21 and over.

The Downtown Special Services District on Monday announced plans to restrict the event to adults of legal drinking age on the advice of Stamford Police, who have arrested disruptive and inebriated teenagers in previous summers.

“We do not do this lightly,” said Sandy Goldstein, executive director of the DSSD. “This is a major change in the concert. It’s going to upset a lot of young people who love the concerts and love the music, but it’s something we know we have to do.”

Goldstein said that while 9 out of 10 youths aren’t problematic, the other 10 percent cause trouble.

“I love the youngsters at the event - especially the ones from Stamford,” she said. “Unfortunately, the ones that come from out of town - not all of them - view it as an event to drink and come into the concert in not very good shape.”

Stamford Police Chief Jonathan Fontneau said last summer’s underage drinking problems are well documented.

When Sister Hazel played in August, for example, almost 10 youths were either brought to the hospital or had to be picked up by their parents. The week before that, a total of 27 youths were held in a “drunk tent” or taken to the hospital after an Andy Grammer performance.

“We want to make sure we don’t create an environment where drinking is accepted,” Fontneau said. “A group of people under 21 years old caused mayhem throughout the city on several occasions and we’re looking to not have another incident.”

Police, the state liquor authority and representatives of the DSSD will check identification at the eight entrances to the concert venue.

Concertgoers will have to present a current driver’s license, identity card issued by the state Department of Motor Vehicles or a passport along with another form of photo ID. The tickets, which cost $10, are not sold online.

Fontneau plans to meet with Goldstein Tuesday to hammer out details for implementing the new restriction. “We’re looking forward to making some changes for the betterment of the concertgoers,” he said.

Last year, Alive@Five brought about 40,000 people into the downtown over the course of six concerts. Roughly a quarter of them came to see Shaggy in the final event of the summer, which was so popular that Metro-North warned riders not to get off the train because Columbus Park was full.

The lineup for this year’s series, which goes from July 7 to Aug. 11, will be announced in May.

Goldstein said attendance is likely to drop since about 25 percent of the attendees in prior years were under 21. “This will have an impact,” she said. “We will have fewer people at the concerts.”

Goldstein said the DSSD is talking about holding an additional concert for younger people.

Alive@Five is run by the DSSD in partnership with Stamford Town Center, Reckson and BevMax.

Stamford area youths craving an urban outdoor music experience will travel into New York City to attend such events as the three-day Governors Ball at Randall’s Island Park in June, predicts Jennifer Bangser, director of marketing and public relations for the Cultural Alliance of Fairfield County.

“They’ll go because they don’t have age limits on them, and they are public,” she said.

Bangser said kids might also be diverted to outdoor concerts in neighboring cities such as Bridgeport, Norwalk, Danbury, Ridgefield and Greenwich, although those series are more family oriented and low key.

If the point of Alive@5 is generating traffic for Stamford’s lively nightlife scene, shutting out teenagers might not be a bad thing, Bangser said.

“Maybe that’s not who Stamford is trying to attract,” she said. “The young professionals have disposable income to go to the restaurants and spend the money.”; 203-964-2263