Doing 200 reps of anything per day doesn't develop strength at all, it develops endurance. Actually, without further increases, after a few days it only maintains endurance.
If you want to develop grip strength, I recommend the Ivanko Super Gripper:
Also, regarding the inevitablity of strength declining with age: That's an old saw based on the fact that most people are lazy and ignorant of productive training methods. I know some powerlifters who are over 70 who are stronger than I'll ever be. Declined from younger levels, yes, but still stronger than 99.9% of the population. There is no reason, with proper training, one can't be very strong and capable into very old age.