I'm supposed to do a cake for a 13 year old girl. The only instruction I got was for it to be an "exploding 13". My question is if I made the wilton's 3d cupcake and put a 13 on top of it with stars coming out of it to make the explosion... Is that going to be too young looking??

Should be fine. Maybe find out what the birthday girl's favorite colors are to incorporate that into the cake.