Personalized 6th Birthday Boy Rocket Youth Long Sleeve T-Shirt. 6th Birthday Boys Rocket Ship Youth Long Sleeve T-Shirt - White in striped blue and white with number 6 on this space themed bday gift. youth long sleeve t-shirt. Shoulder-to-shoulder taping. Youth: S(6/8), M(10/12), L(14/16), XL(18/20)