Answer by taking a quote from the following article:

Dion Francis DiMucci (born July 18, 1939), better known mononymously as Dion, is an American singer, songwriter whose work has incorporated elements of doo-wop, rock and R&B styles--and, most recently, straight blues. He was one of the most popular American rock and roll performers of the pre-British Invasion era. He had 39 Top 40 hits in the late 1950s and early 1960s as a solo performer, with the Belmonts or with the Del Satins. He is best remembered for the singles "Runaround Sue", "The Wanderer", "Ruby Baby" and "Lovers Who Wander", among his other hits.

Bob and Gene Schwartz also signed Dion's friends, the Belmonts, (Carlo Mastrangelo, Fred Milano, and Angelo D'Aleo), a vocal group named for nearby Belmont Avenue, and teamed them, with Dion singing lead. The new group's breakthrough came in early 1958, when "I Wonder Why" (on their newly formed "Laurie" label) made No. 22 on the U.S. charts. Dion said of the Belmonts; "I'd give 'em sounds. I'd give 'em parts and stuff. That's what 'I Wonder Why' was about. We kind of invented this percussive rhythmic sound. If you listen to that song, everybody was doing something different. There's four guys, one guy was doing bass, I was singing lead, one guy's going 'ooh wah ooh,' and another guy's doing tenor. It was totally amazing. When I listen to it today, oftentimes I think, 'man, those kids are talented.'"  Their initial hit was followed by "No One Knows" and "Don't Pity Me," which also charted the Billboard Top 100. This success won a place for Dion and the Belmonts on the ill-fated "The Winter Dance Party" tour with Buddy Holly, Ritchie Valens, the Big Bopper (J.P. Richardson), Frankie Sardo, and other performers. On February 3, 1959, after a concert stop in Clear Lake, Iowa, Holly and others decided to charter a flight to the next venue rather than travel on the tour bus. Dion was invited to accompany the group but decided that he did not want to spend $36 for the flight, as it was the same monthly rent his parents paid for his childhood apartment and he couldn't justify the indulgence. The plane crashed, killing all on board; Holly, Valens, Richardson, and the pilot Roger Peterson. Dion and the Belmonts continued on the tour, along with Frankie Sardo, while Bobby Vee, then an unknown artist, performed in Holly's place at the very next concert. Later, Jimmy Clanton, Frankie Avalon, and Fabian were added to replace the other now-deceased headliners.  Dion and the Belmonts' next single, "A Teenager in Love," was released in March 1959, eventually hitting No. 5 on the U.S. pop charts and No. 28 in the UK. The group's biggest hit, "Where or When," was released in November of that year, and reached No. 3 on the U.S. charts. However, in early 1960, Dion checked into hospital for heroin addiction, a problem he had had since his mid-teens. Further single releases for the group that year were less successful. There were musical, personal and financial differences between Dion and members of the Belmonts, and in October 1960, Dion decided to quit for a solo career. By the time of their breakup, all eight Laurie releases had charted on the Hot 100.

How old were the members of the group?
No One Knows