READ THIS NEXT: Former Child Actor “Was in Danger” on Movie Set, Co-Star Admits. Allen was such a pro at being a young Garner, she was invited to try her hand at it again a few years after 13 Going on 30. In 2009, she played Garner’s character Jenny as a teen in the rom-com Ghosts of Girlfriends Past, co-starring Matthew McConaughey. She told Entertainment Tonight last year that the older star recommended her for the role. “I will just say that me playing her in Ghosts of Girlfriends Past was a function of Jennifer speaking up. They were looking to cast the role and they were like, ‘We don’t know what to do. We’re trying to find a younger you,’ and Jen was like, ‘Call up Christa. She’s done this before and she’s good at it,’” Allen told the outlet. “So I really owe that role to her as well. And that’s again, just speaking to her kindness.” Obviously, no actor can make a complete career out of being another star’s younger doppelgänger. Since 13 Going on 30, Allen has appeared in TV shows including Grey’s Anatomy, ER, Wizards of Waverly Place, Baby Daddy, and Code Black. She was one of the stars of the drama series Revenge, playing Charlotte Grayson from 2011 to 2015. She’s played parts in feature films including Youth in Revolt and The Valley, as well as several TV movies, the most recent of which was 2021’s Christmas for Keeps. Between roles, Allen is conquering social media. The actor has nearly 2 million followers on the video app TikTok, where she posts everything from getting ready videos to fit checks to comedy sketches. In one 2020 video, which went viral beyond users of the app, Allen celebrated Halloween by donning her costume—adult Jenna’s multicolored dress that she wears to a magazine party—to a soundtrack of Whitney Houston’s “I Wanna Dance With Somebody,” the same song the montage is set to in 13 Going on 30. She’s also recreated other famous ensembles from the movie on TikTok, stunning fans with how much she looks like Garner now that she’s all grown up. As it was for a lot of entertainers and regular people alike, it was the pandemic that attracted Allen to TikTok. “Because the industry was basically shut down, especially in the beginning, we just didn’t know what was going to happen,” she told Allure last year. “I was like, this TikTok thing has some momentum. If I do TikTok like it’s my job, it’s going to become my job, and it has.” For more celebrity updates sent right to your inbox, sign up for our daily newsletter. Last year, looking ahead to her 30th birthday, Allen wrote an essay for Allure about finally reaching that milestone her teenage character was so looking forward to. The actor says in the piece that she’s always felt a connection to “people turning 13, 30, and everyone in between,” adding, “I have become a mirror of sorts, reflecting back to them the intense feelings they have about reaching these ages.“ae0fcc31ae342fd3a1346ebb1f342fcb But, Allen also writes that she was “conflicted” about acknowledging her birthday, because she doesn’t think that a person’s age is all that important. “The world is so eager to define us by age, and I know that another person’s attempt to define me or put me in a box based on my age or any other number associated with me is a reflection of them, not of me,” Allen says in the essay. “But what is age but energy? I like to think of my energy as ageless.” READ THIS NEXT: See Young Jenny From Forrest Gump Now at 37.