“It’s my gift to the world: I make people feel old. I’m no longer a kid, that’s my job,” the actor joked on Twitter.

Macaulay Culkin. PHOTO: KIMBERLY WHITE/GETTY IMAGES

Macaulay Culkin celebrated his 40th birthday on Wednesday — making his fans feel “old” by jokingly pointing it out.

The Home Alone star joked that since he is “no longer a kid,” his job is now to “make people feel old.”

“Hey guys, wanna feel old? I’m 40. You’re welcome,” he wrote on Twitter, adding, “It’s my gift to the world: I make people feel old. I’m no longer a kid, that’s my job.”

Culkin’s girlfriend, Brenda Song, also took to social media to mark his milestone birthday.

“Happy 40th birthday to this magical being,” Song, 32, wrote on Instagram, sharing a photo of the couple wearing matching plaid PJs.

“I could sit here and write endlessly about how wonderful, kind, loving, genuine, loyal, honest, brilliant and hilarious you are, and how grateful I am that I get to share and do this life thing with you,” Song wrote.

“But firstly, that would take me an eternity and secondly, you won’t even see this because you don’t ever use instagram. Hahaha.”

“My unicorn that I never thought could exist, I am luckiest person in the world because I am loved by you,” the actress added.

Culkin’s next chapter will see him return to his acting roots — albeit in a much more adult role than those that made him a child star.

Earlier this year, it was announced that Culkin will join Sarah Paulson and Evan Peters in the tenth season of American Horror Story.

In May, AHS creator Ryan Murphy revealei some details about Culkin’s role.

“I have always loved Macaulay Culkin’s work,” Murphy said in an interview with E! News.

“I loved everything that he’s done, I love the stuff he did in Home Alone, I also loved the sort of the older, more recent stuff that he did. And he hasn’t worked in a while.”

“So, I have this very, very great insane part. And I asked to speak to him on the phone and he said OK,” Murphy said. “[When] I cast, I never let people read things, usually. I said, ‘OK, here’s the pitch.’

And I told them the character and I told him he has crazy, erotic sex with Kathy Bates and does other things.

And he paused and he goes, ‘This sounds like the role I was born to play.’ So, he signed up right then and there.”

“There’s both a lightness and a darkness with Macaulay Culkin that I’m attracted to,” Murphy added.