Anybody can knock down shots when wide open, regardless of age/position/size. The fundamentals can only take you so far though.
In game situations require you to remain composed, you have to create enough space, rush your release affecting your form. What separates NBA guys from non NBA guys is the ability to create space on offense. Space is basically the distance between you and the defender, how well they're able to contest your shot.
Space can be created through ball handling, crossing a guy up and forcing him off balance, leaving you open for an easy shot. Moving without the ball like Danny Green, fakes/footwork such as Duncan or Melo on the perimeter, bodily contact like Kawhi Leonard or Z-Bo, etc.
Plenty of guys such as myself, can shoot lights out, but I cannot do the other stuff that'd allow me to get my shot off during an in game situation at will like NBA guys.