Son, go ahead and train shoulders using sub-maximal weights for even one month and see how well your shoulder and chest workouts are going by the fifth week.
Sarcasm is just in the begining stages of learning still. Being sixteen, he's only able really handle weights that dont really put any stess on the joints yet. 50lb db presses, 25lb poor form laterals, 40lb upright rows... Skipping workouts and training with sloppy form, he still hasnt yet harnessed the ability to use weights to their full potention cause he's still learning how to train. (I'd like to see lil Sarcasm hit the "Gaybex" full stack with a 45 on it)
Come back when your pushing some weights,,,, like all these pro's are capable of doing,, then let we'll talk about not using machines here and there and supplementing some lighter routines into your program to obstain from overtraining and injury.