Maci Bookout attends The Candie's Foundation Event To Prevent on May 5, 2010 in New York City. Credit: Joe Kohen/

Maci Bookout's son Bentley is growing up fast!

Turning four years old on Oct. 27, Bentley, the Teen Mom star's son with ex Ryan Edwards was feted with a cowboy-themed bash that would make any other boy his age jealous.

"My little cowboy turned four today!! such an awesome day!" Tennessee-based Bookout, 21, tweeted on her son's big day, posting a pic of him dressed up in an adorable checkered shirt, straw hat and red bandana. "He is my perfect world."

On the agenda for Bentley's big bash: Horse rides, a petting zoo, and -- breaking with the cowboy theme -- a motorcross-inspired birthday cake!

Welcoming Bentley in 2008 with ex Edwards, Bookout calls her son's birthday celebrations one of the toughest times to be a single mom, because she has to share custody of him with his dad.

"Birthdays and holidays are the hardest because we have to share him, but coparenting with Ryan is getting better," Bookout told Us Weekly in August.