Aniston's friends agree that she makes 51 look pretty great.

\"No matter how hard you might try...there’s only one Jennifer Aniston,\" Courteney Cox wrote on Instagram. \"Happy birthday my dear friend [Jennifer]! I love you!\"

Meanwhile, Aniston's ex-husband Justin Theroux shared a photo on his Instagram Story of Aniston making a fist. He captioned it, \"grabbing 2020 & another year just like -- HAPPY BIRTHDAY B.\"

For more posts dedicated to Aniston, see below.

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No matter how hard you might try... there’s only one Jennifer Aniston. Happy birthday my dear friend @jenniferaniston! I love you!♥️♥️♥️

A post shared by Courteney Cox (@courteneycoxofficial) on Feb 11, 2020 at 12:16pm PST

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Happy Birthday Jen! 🌟 I couldn't ask for a better friend and partner to chase my dreams with. Life is way more fun with you in it!!! 💯❣️

A post shared by Reese Witherspoon (@reesewitherspoon) on Feb 11, 2020 at 8:53am PST

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Happy birthday, Jenny!!!

A post shared by Matthew Perry (@mattyperry4) on Feb 11, 2020 at 1:24pm PST

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Happy birthday, @JenniferAniston. I can't wait for our slumber party tonight. Portia bought Mad Libs!

A post shared by Ellen DeGeneres (@theellenshow) on Feb 11, 2020 at 1:46pm PST

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Sweet angel woman, light of so many lives, the babelicious bird who takes care of all in her nest, @jenniferaniston happy birthday to you!!! We love you!!!! 🎂🎂🎂💕💕💕

A post shared by Rita Wilson (@ritawilson) on Feb 11, 2020 at 9:07am PST

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