There’s a universe of difference between the splitter and the forkball. I do believe that when someone talks about the grip being injurious to a pitcher’s arm or shoulder he’s really referring to the forkball—that’s the one where the fingers are spread so wide they’re on opposite sides of the ball. For that you really need to have large hands and very long fingers, and I don’t believe that’s the case here. Now, for the splitter—you can grip the ball as for a two-seam fast ball and then spread your fingers just wide enough so they’re off the seams, and that will do the trick. But you have to throw it the same way you do a fast ball.
I think you might have an easier time with the slider than you realize. To begin with, the grip is off-center—niether two-seam nor four-seam, but somewhere in between. You can experiment until you find the right spot. As for throwing it—I had a pitching coach years ago who was absolutely incredible, and what he told me was “Throw it like a curve, but roll your wrist, don’t snap it.” You know how you throw a curve with a wrist snap like a karate chop or pulling down a window shade? Well, for the slider you just turn it over, and the wrist action is easier. I learned that pitch when I was sixteen, and in a short time it became my strikeout pitch, the one I could really go to—so I don’t think you’re too young to try that one.
Other pitches you might experiment with: The palm ball, which is what it name implies—you grip the ball way back in the palm of your hand, but not so far that it gets stuck there, between your thumb and your little finger with the other three fingers on top of the ball—hence the name.
And you throw that one just like a fast ball. You can turn it into a changeup by loosening the grip. In fact, my coach told me that just about any pitch you throw can be turned into a changeup. The knuckle-curve is another nice pitch to add to your arsenal—you grip it like your usual curve but then you turn your middle finger in so that your fingernail is dug into the seam. It’s sometimes called a “spike” curve, and that’s how Mike Mussina throws it. (A good incentive not to bite your nails.) I could tell you a lot more, because when I pitched I threw a lot of “snake jazz”, not having a fast ball to speak of—but I think you have something to start with. Have fun. :baseballpitcher: 
