I am trying for a few months now. But my forearm size is definitely has not changed much. When I started it was 11" now 13" (3 months period). Now my Target is to achieve atleast 17" if possible 20-23" in next 3 years. Mean while my arm has blown up. It was 13" when I started currently 17". Feel like it’s an extremely disproportionate growth. (Growth Difference of 2").
My workout routine is followes.
Wrist extension & flexion, static standing, rope hammer curl, rope reverse curl. 5x15, 3 times a week with 48 hours gap
I dont think you have a handle how big a actual 20- 23 forearm is. Or how much overall bodyweight and mass you’ll need to gain for a additional 10 inches .
Ditch the rope
Adjust exercise order
Lower the reps
Rest longer between workouts
Check out this example from Charles Poliquin
EZ Bar Reverse Curl x 6-8 reps, 5 count eccentric, rest 10 seconds
DB Hammer Curl x 6-8 reps, 4 count eccentric, rest 10 seconds
EZ Bar Reverse Curl x 6-8 reps, 5 count eccentric, rest 2 minutes
Do 3 rounds. Give your arms 4 days to grow then train again on the 5th day.