Prepare to feel ancient because the adorable baby from Disney Channel's Good Luck Charlie is now officially a high schooler.

Mia Talerico, who played Charlie Duncan in four seasons of the popular TV show and its Christmas movie, posted a first-day-of-school photo on Wednesday (Aug. 23) that left fans feeling seriously old.

See the baby from Good Luck Charlie today:

"She’s so big! Mia, you’re beautiful!" Leigh-Allyn Baker, who played Charlie's mom Amy Duncan on the show, commented on the photo.

Fans also marveled at how much the child star has grown up since her Good Luck Charlie days.

"We have been preparing you for this moment your entire life bookie!! GOOD LUCKKKK!!" one fan commented.

"Wait she's already in high school now omg I feel so old right now and I'm only 19," someone else wrote in the comments.

"Casting in Good Luck Charlie was SO GOOD. Like she looks so much like Teddy/ Bridgit Mendler it’s crazy," another person noted.

"Y’all lying if she fr in hs. Ain’t no WAY. Good thing u got them video diaries from Teddy," someone else joked.

"Have a great school year and most importantly good luck Charlie," another fan wrote, referencing the iconic line that concluded all of the video diaries in the show.

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Good Luck Charlie premiered on Disney Channel in April 2010, and began when Talerico was only 11 months old. The show followed the Duncan family as they adjusted to having a new baby in the house.

On the show, actress and singer Bridgit Mendler played Charlie's older sister Teddy, who makes video diaries featuring life advice for her little sister.

The family show went on to run for four total seasons, ending in 2014 after adding another baby named Toby to the mix.

Since then, Talerico has continued acting in television, including a role in the series Mani and a role in the series Conrad.

In 2020, she reunited via Zoom with her Good Luck Charlie co-stars to celebrate the 10-year anniversary of the show for Entertainment Tonight.

"I probably had a really easy role 'cause I just got told most of my lines or didn't have any. I think it was really easy because most of the time, it was what happened. We just rolled with it, like, in the crawling scene, I just stood up, so we just went with it," Talerico shared.

As for a future reboot of the series, Talerico suggested a grown-up Charlie could find Teddy's videos.

"I always felt like if we did do one, where I found Bridgit's video diaries ... that's what I was always thinking, if that did happen," she said.

Popular Child Stars From Every Year

Below, Stacker sifted through movie databases, film histories, celebrity biographies and digital archives to compile this list of popular pint-sized actors from 1919 through 2021.