Ganglion cysts form on tendons and you do have tendons in your fingers but ganglions tend to form more on the back of the hand. It is possible but it should hurt the movement of your finger as it constricts the movement of the tendon in that small area.
However, good old plain osteoarthritis, the arthritis of aging, tends to form lumps and bumps all around your finger joints. They are painless and just there, usually near the joints and sometimes on them but they don't hurt and usually don't even interfere with motion. They start very small so you feel but not see them and then will slowly get bigger. And they can start young if you've ever had an injury to that area or like me, you knit and crochet. All sorts of handiwork can cause the bumps to start earlier.
Bet you anything that is what you are feeling. I have them all over my fingers.
Ask your doc the next time you're in.