Iain Armitage may be known to many as Young Sheldon‘s titular character, but he is anything but little now.

Ahead of his 17th birthday on Tuesday, July 15, Armitage surprised his social followers by looking all grown up in an Instagram mirror selfie. “Summer nights…” he captioned the snap, which featured him smiling into the camera and sporting a snazzy suit.

Many were surprised by the actor’s more mature appearance after being introduced to him at the age of 9 in Season 1 of Young Sheldon in 2017. “Young Sheldon not young anymore, a handsome young stunning man 🙌🔥,” one person commented underneath Armitage’s Instagram post.

One user joked, “Is that the same guy who was in young Sheldon? More like tall Sheldon 😮,” while another added, “STOP GROWING UP!!!!”

A different user compared Armitage to one of Hollywood’s biggest stars, writing, “Bro startin to look like Tom Cruise😂.” Another person, meanwhile, stated that Armitage resembles Young Sheldon’s Pastor Jeff (Matt Hobby) “in his younger days.”

One commenter noted that Armitage has evolved into the older version of his famous sitcom character. “Young Sheldon is now Sheldon,” they shared.

Several fans filled the post’s comments with early birthday wishes for Armitage, as well. “Happy Birthday Iain!! I hope you have a wonderful day and a wonderful year? 🤗👍🎂 @iain,” one person shared, while someone else commented, “Happy 17th birthday bro ❤️.”

“Happy Birthday, @Iaian! Wish you all the best and success in all your projects,” a different user wrote underneath the post. A separate person shared, “Have the happiest birthday Iain 🎂 Wish you all the best 💞.”

On Tuesday, Armitage commemorated his 17th birthday by sharing a pic of himself holding a birthday cupcake. “Thank you thank you thank you for all the birthday wishes!!!” he captioned the celebratory snap.

In another Tuesday Instagram Story pic, Armitage smiled for the camera before blowing out a birthday candle in a frozen treat. “Thank you, everyone!” he told his followers. “I’ve seen (and loved!) your messages. It’s been a wonderful day and I’m so grateful!”

Armitage appeared in shows such as Law & Order and Big Little Lies before making his debut on the spinoff of The Big Bang Theory, Young Sheldon, in 2017. The show about Sheldon Cooper’s (Jim Parsons) childhood wrapped its seven-season run in May 2024. It launched another CBS spinoff, Georgie & Mandy’s First Marriage, which premiered that October.

Since Young Sheldon‘s conclusion, Armitage has obtained his pilot’s license and completed his first solo flight in July 2024 and has visited Congress to advocate for arts funding with The Creative Coalition earlier this year.