Hilary Duff's Son Luca Is Officially a Teenager as She Celebrates His 13th Birthday in Heartfelt Post: 'Being Your Mom Is the Best'

Hilary Duff's son is officially a teenager!

On Thursday, March 20, the Younger star, 37, shared a heartfelt post on Instagram celebrating her son Luca Cruz turning 13. In the post, Duff shared a carousel of solo shots of the teen throughout the years, mixing in a few with photos with his sisters and a throwback image of the pair in the delivery room.

"Wow- is time ever a thief. I thought ten years of being a mom felt wild…yet here I am at my son’s 13th birthday," she began her heartwarming caption. "I can’t go anywhere without people telling me what a nice kid Luca is. Sweet, heart facing forward with the coolest point of view. He can talk anyone under the table about soccer, players dating back to the 70’s, specific games that defined history…He’s an amazing creative drawer, a beautiful writer (hopefully more of that in the future) and I *think* taking a new interest in history☺️."

"Its been so fun listening as he talks about the world’s history - since I didn’t have an 'normal' schooling experience.. there are definitely some gaps & it’s sure cool to have the tables turned and see how much more he knows more than me…Just in this one instance of course 😉," she continued. "It’s so cool to see his interest shift, his confidence grow…his sure footedness and knowing being learned."

Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer​​, from celebrity news to compelling human interest stories. 

"My only son. I love you more than the moon and as far as all the stars in the sky. Hanging with you is the best. Getting a text from you .. the best. Talking late and snacking in the kitchen is the best. Driving you is the best (even though you forget all your s---)," she said. "Watching you play soccer is the best. Listening to hip hop with you is the best (let’s gooo Kendrick and lil tecca). The kind of big brother you are is the best. Your smile is the best. Your humor is the best. you being fully YOU is the best. Being your mom is the BEST. HAPPY 13 Angel , forever standing by to cheer you on. ♥️ -mom."

The How I Met Your Father star first welcomed son Luca in 2012, with her then-husband Mike Comrie. Following their split, Duff began dating Matthew Koma. The pair got married in 2019 and welcomed daughters Banks Violet, 6, and Mae James, 3, in 2018 and 2021, respectively. In December 2023, Duff announced she was expecting her fourth child, and Townes was born in May 2024.

In an interview with PEOPLE in May 2021, Duff revealed that she loves the "mayhem" of raising her kids. "I love when everyone's full of energy and the house is buzzing. You never know what the day is going to bring or what your kid's going to say," she said. "We're in the thick of it, and it feels good."

During an episode of The Motherly Podcast, Duff opened up about her experience welcoming her first child at 24 years old. While at first it was pretty “isolating," the mom of four said welcoming her son Luca changed everything in her life — and not necessarily in a bad way.

Duff said being a mother has been “shocking and it was also the happiest, most beautiful experiences, so those two things butting up against each other is quite a strange mix sometimes.” The Lizzie McGuire alum admitted to losing her identity for about a year and a half, before getting it back and growing stronger.

“Once you do find yourself again, you have the biggest thing under your belt that nobody can take away from you and you’re so confident,” Duff said of getting her identity back.

“I did spin it as a positive thing because sitting in it when it was happening maybe I was a little sad about it and I didn’t feel like I had anyone to go through the experience with, but then I came out on the other side," she continued. "I’m like, I’m a freaking super woman and I can do anything and I have confidence for days.”