You know you’re getting old when a teenager today thinks The Knack is a new band.

The thought has Doug Fieger beaming.

“It’s funny and intriguing,” the lead singer-songwriter said recently from his Los Angeles home. “A number of my friends have teenage kids who are playing our records and are completely unaware that we had happened before.”

One of those friends is actor Tom Arnold, who called Fieger up a few weeks ago to congratulate him on the chart rebirth of The Knack’s 1979 No. 1 smash “My Sharona.” Perhaps the quintessential power-pop hit of the Me Decade, “My Sharona” has been given new life with its inclusion in the Ben Stiller movie “Reality Bites.”

“Tom says his stepson was playing the (soundtrack) album, really rockin’ on it and playing ‘My Sharona’ over and over again,” Fieger says. “So he tells the kid, ‘That guy was at your bar mitzvah,’ and he’s like ‘No way!’ Tom says, ‘That record was a hit when I was a young man.’ ”

Fieger’s friendship with Arnold goes back five years when mutual friends introduced them. Since then, Fieger has rediscovered the acting bug and appeared in several episodes of TV’s “Roseanne,” starring Tom’s wife.

“I’ve actually had lines and everything,” Fieger says. “I was one of the poker buddies of John Goodman. In fact, I was in the episode when Tom’s character, Arnie, came back from the space aliens and wanted to get back with his ex-wife, Sandra Bernhard, and she tells him she’s gay.”

A Shakespearean-trained actor, Fieger – now in his early 40s – set aside acting classes in his early teens to pursue music, forming the rock trio Sky in his native Detroit.

“We used to open shows for a lot of the major acts like Traffic, Joe Cocker, Jethro Tull, The Who, Alice Cooper,” Fieger says. “Here I am only 15 or 16 and I’m meeting all these great musicians.

“When I was in the 12th grade, I wrote a letter to the producer of Traffic and Rolling Stones, Jimmy Miller, and said ‘if you’re ever in Detroit, come and hear my band.’ He not only answered the letter, he came to Detroit, came to my house and heard my band down in my basement and then signed us.”

A week after his high school graduation, Fieger was in a London studio, recording Sky’s debut RCA album, while the Stones were next door cutting “Sticky Fingers.”

Sky managed only two albums, then Fieger moved to L.A., eventually hooking up with guitarist Berton Averre, drummer Bruce Gary and bassist Prescott Niles to create The Knack.

For the uninitiated, The Knack was the definitive overnight sensation in 1979, rising from bar-band status to become the press-dubbed “new Beatles.” With its irrepressible driving beat, “My Sharona” logged six weeks at No. 1 and stuck out like a sore thumb amid the disco domination of Chic and Donna Summer.

It took less than a month for “Get The Knack,” the band’s debut album, to sell more than 1 million copies. Just as quickly, The Knack was assailed by the critics and accused of being pre-fabriciated.

Nothing gets Fieger’s blood boiling more.

“I would read that we were this manufactured thing that was foisted on an unsuspecting public,” he says. “Nothing could be further from the truth. We were a real band that began as an art project and then everything that happened after that was organic.”