10/19/2008 at 04:00 PM EDT
It's party time for Zac Efron
The star of High School Musical 3: Senior Year
celebrated his 21st birthday Saturday with an intimate two-hour dinner party at L.A.'s Pace restaurant with a group of friends and family that included his parents and brother, girlfriend Vanessa Hudgens
costars Monique Coleman and Ashley Tisdale
, her boyfriend Jared Murillo and pals Michelle Trachtenberg, Amanda Bynes
, Brittany Snow and singing sisters Aly and AJ Michalka.
Efron kept it causal in a T-shirt and jacket while Hudgens, 19, who "helped plan the party," a source says, donned a colorful mini-dress. Guests arrived with wrapped gifts, including bottles of liquor for the actor, who can now legally drink alcohol.
Efron and Hudgens left the rustic Italian eatery hand-in-hand just before midnight and disappeared into a waiting car. But the celebration continued at a nearby hotel, where the birthday boy hosted an afterparty with some of his dinner guests.
At the HSM3
premiere in L.A., Efron's friends and costars were mum on the night's festivities. But Efron pal Bubba Lewis told PEOPLE, "We'll probably go out, eat some food, laugh, have a good time."
Costar KayCee Stroh echoed Efron's desire for a low-key celebration. "We're definitely going to party it up," she said. "But he's that guy that would rather sit down with friends and have a good discussion than deal with the craziness."
And what to get the guy who has everything? "I'm going to get him tinted windows," says Stroh. "That's what I gave Miley Cyrus for her birthday and he's getting them too."
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