Birthday Girl Kylie Jenner, 15, Has Grown Up 'Way Too Fast,' Says Big Sister Kim Kardashian

Kylie Jenner has become quite an impressive young woman since she first appeared on "Keeping Up With the Kardashians" in 2007.

On August 10, Jenner turned 15 years old, prompting her older siblings to reflect on the young model's growth over the past five years.

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Calling her "stunning, silly, smart, talented and funny," Kim Kardashian, 31, blogged that Jenner is "growing up way too fast for my liking, but what an amazing and beautiful young lady [she has] turned into. We are all so proud of [her] and I can't wait to see what the future has in store."

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Kourtney Kardashian -- see exclusive photos of her newborn daughter, Penelope, in the new issue of Us Weekly, out now! -- also praised Jenner on her official blog. "You are filled with so much fun and happiness but so nurturing and understanding at the same time. You have wisdom beyond your years and I'm proud to call you my sister," the 33-year-old reality star wrote. "I love you madly. I hope all of your birthday wishes come true."

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"How are you 15?" Khloe Kardashian, 28, wrote in a tweet directed at Jenner. "There's no one like you in the world! Never change! I love you!"

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