The splitter requires the index finger and the middle finger the spread along the sides of the baseball, mostly following the seams running up-n-down, much like the seams on a two seam fastball. The desired effects of the pitch can vary depending on the strength of the pitcher’s grip, forearm and pitching side of the shoulder. In fact, a lot of stress is supported by the grip and pitching side shoulder, with the elbow sometimes getting lost in the motion. Like I mentioned, this pitch requires a lot of concentration and maturity.
Perhaps the youngster that you’re referring doesn’t have the muscular frame and physique to handle these stresses loads, or some other consideration, physically.
On the other hand, look at the purpose and signature of this pitch and the intended effect after release, down range to the batter. This pitch requires a lot of concentration and deliberate mind of purpose. It’s not for everyone.
I wouldn’t recommend this pitch to a youngster who’s still learning to control and locate pitches. I only say that because it’s time consuming to coach, learn and most of all being consistent with its intent and results. Most of the time with youngsters still in the develop stage of their physical maturity; use this kind of pitch as an awkward off-speed pitch.