Ok, My dad is a great pitcher. He can throw all kinds of pitches from a fastball to a knuckleball. One pitch I like is his splitter. Do u recomend I throw a splitter yet? I’m 13

As long as you don’t twist (i.e. supinate) the wrist, it’s ok. Keep the thumb centered between the two fingers to reduce the tendency to supinate.

Unless you’re wanting to throw this as an alternative to the change-up, I would focus on the change-up instead because I think the splitter is more difficult for young kids to throw than the change-up. You don’t need both pitches, IMHO.