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Justin Bieber

Ethan Miller/Getty Images

Justin Bieber is a baby no more.

Today, the teen idol turns the big 1-8. "I feel so much different," he joked to Ryan Seacrest on KIIS-FM. "I'm just kidding man. It's been crazy, man... Just the amount of people that have hit me up and giving me birthday wishes. It's been amazing."

And even though J.B. is now a legal adult, he hasn't lost his love for childlike pranks. He recently played a dirty trick on pal Taylor Swift for MTV's Punk'd...

Gallery: Justin & Selena...Aww!

In the trailer, Justin coaxes the country star into setting off fireworks. Then much to Taylor's dismay, their fireworks [appear to] land on a boat where a couple is getting married, causing the wedding party to abandon ship and swim to safety. "This is completely not OK," she cries.

The Biebs cracks up as Taylor, relieved, tells him, "You are the worst!"

But even though J.B. is joshing around on TV, is he ready to settle down in his real life with girlfriend Selena Gomez?

Umm, not so fast.

"First and foremost, I'm not engaged," he told Ryan this morning when asked about the sparkly "J" ring his girlfriend tweeted a photo of on Valentine's Day. "You know, we're still young, so at this moment in time, this is where I am. So that's all I can really say."

Ryan Seacrest

2012 Ryan Seacrest/Whosay

Hear that Beliebers? And look, even though he's now technically a "grownup," he's still the same precocious teen.

He took a moment to address his more mature fans on Twitter: "dear cougars. im legal. i see the jokes. hahaha."

In any case, as Ryan is the consummate host, he couldn't let his guest off without offering up a gift to the birthday boy, which he showed off on his WhoSay page. So, did he deliver the goods? Oh, yeah.

What 18-year-old doesn't want a Costco gold membership card?

Get More: MTV Shows