The party was held this past weekend and was attended by her wife, Violet and  a number of their close friends.
The couple dressed down for the occasion, sporting tracksuit tops as they posed for pictures and laughed with friends.
And, of course, what would an Olympic gold medalist's birthday be without a cake shaped in a giant running shoe!
The party was held on the same weekend as Caster and Violet's wedding. The pair were married at the Chez Charlene wedding venue in Pretoria, surrounded by friends and family.