HOLLYWOOD, California -- At only 21 years of age, [movieperson id="438080"]Zac Efron[/movieperson] has already attended too many massive celebrity events to count. But on Tuesday evening, as he walked down an ear-piercing red carpet to attend the world premiere of his first leading-man movie, the [movie id="365329"]"17 Again"[/movie] star was enjoying a truly special evening.

"It's crazy, and it's different when it's your hometown," the San Luis Obispo-born star explained, looking around at the shrieking crowds surrounding Grauman's Chinese Theater. "I drive across this street all the time, and it's [usually] empty."

"Pretty much anywhere you go with Zac, it's like Beatlemania; it's a little bit like 'A Hard Day's Night,' " marveled "Reno 911!" funnyman [article id="1609052"]Thomas Lennon, who plays Zac's best friend[/article] in the flick. "There's a tremendous amount of screaming and running."

The film appeals to both young and middle-age audiences with a plot that has 37-year-old Mike O'Donnell (Matthew Perry) transforming into a hip 17-year-old high schooler (Efron). Naturally, the carpet was a similar mix of Hollywood veterans (Perry, Lennon, Judd Apatow) and a who's who of teen favorites (the Jonas Brothers, Amanda Bynes, Mitchel Musso, the cast of the upcoming "Fame" movie).

"Zac Efron is hot for my wife! What do I do?" laughed "Knocked Up" director Apatow, whose spouse Leslie Mann plays Efron's love interest in the film. "I'm trying to take the heat that he creates with her and take it back to my house."

Zac Efron At The '17 Again' Premiere

"Tonight is my first time watching the film all the way through in English," Zac said moments before heading inside, explaining that he had only seen the flick in French while overseas. Playing down his above-the-title debut, the "High School Musical" star insisted, "This is definitely not all on my shoulders. ... It's very much a fantastic ensemble piece."

But to hear his co-stars tell it, Efron is lucky to be around for the opening of "17 Again," after he required emergency surgery during shooting. "[Zac was] rushed to the hospital and almost could have died," Lennon recalled of the day on the set in January 2008 that Efron spent in increasing pain before finally being rushed to the hospital for an appendectomy. "Zac's got a high threshold for pain [but something was wrong]. ... So, I told him to just go hang himself upside-down and fart."

"The first week we were working together he was having stomach pains; he was doubled-over between takes," Mann remembered. "The next day, we found out that his appendix burst. ... He went to the hospital and had it taken care of, and he was back at work the next day!"

"Tom was giving me all kinds of advice [when I was in pain]; he brought up packets of Beano and was like, 'Here, take this,' " Efron laughed, happy that the whole event was behind him and that he'd soon be heading inside to watch the fruit of his painful memories. "I felt like an alien was going to pop out [of my stomach]."

Check out everything we've got on "17 Again."

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