Brad Pitt hates celebrating his birthday because it reminds him he is getting older.

The "Ocean's Thirteen" actor - who turned 44 on December 18 - is reportedly plagued by insecurities about his aging body and told lover Angelina Jolie not to buy a birthday cake last month.

A source told America's Star magazine, "A birthday greeting from Brad's sister Julie was met with a grumpy, 'Don't remind me!' He doesn't like to be reminded about getting older. He didn't even want a birthday cake. He's says, 'It's my job to look good.'"

"The obsession with his looks has gotten worse very recently. It's hit him pretty hard that he's not looking as young as he was. When he first hit Hollywood, Brad's natural good looks helped him immensely, but as he has gotten older, he is finding it more and more difficult to maintain them."

Brad is said to be attempting to recapture his youth by racing around on the $100,000 custom-built motorbike Angelina bought him for his birthday.

The source added, "He makes sure to ride every day. It makes him feel young. It's the rebel in Brad. It's hard for him to let go."

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