Hey there. The independant movement of ring and pinky fingers seems to be a universal issue. I remember many years ago starting out at piano lessons. One of the challenges was to get rings and pinkies moving independant of each other. The problem stems from the fact that they share a common tendon. The other fingers have a tendon each (think this is correct!). But with training you can achieve a fair amount of individual strength and movement.

Keep at it.

Alf (a fellow older adult)