Luke Bryan's son Bo is almost all grown up. He turned 16 years old on Monday (March 18).

The country superstar's wife Caroline celebrated the milestone with a nostalgic social media post, sharing a montage of photos of Bo through the years. There are throwback photos of a young Bo smiling for the camera and sharing a double stroller with this younger brother Tate, plus more recent shots of him posing with friends and his parents, looking more like the young man he is today.

Caroline also included one very early photo: One of a newborn Bo reaching out and gripping his mom's index finger. From the look of the bed sheets and the paper bracelet around Caroline's wrist, that photo hails from the hospital stay where Bo was born.

"I annoy the crap out of you...but the first time you gripped my finger...my heart melted and I knew I'd never be the same," she wrote.

"Happy 16 birthday Bo!!" Caroline added elsewhere in her post. "The years have flown by and I'm beyond proud of you."

Over the past year, Bo got his learner's permit -- which means the country star parents have been busy teaching him how to drive. Last June, Bryan admitted that the process has been a "nightmare," and that building up his son's driving skills took more time and patience than he'd expected.

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Still, Bo has been slowly getting better: As of December, the Bryans were in talks about what kind of vehicle to get him for his very first car.

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Bo is one of two biological children that Bryan and his wife share, also including younger brother Tate, who is 13 years old. The country couple also adopted Bryan's nephew Til and nieces Kris and Jordan after their parents died. In 2007, the singer's sister Kelly Bryan Cheshire died of unknown causes. Her husband Ben later died of a heart attack in 2014.

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Gallery Credit: Carena Liptak