Age - I havent had probs with any of the clutches on the ducati's I've ridden - but I am left handed, so much stronger that side. (even the old cable clutch on Als Lawson isn't a prob, and that has caught a few chaps out
)
I used to get horse riding clients to strengthen their hand muscles on the weaker hand by clenching & releasing a tennis ball (or similar) - this can be done whilst watching TV, drinking coffee ad infinitum.
(do balance up by using in both hands tho)
after about 4 - 6 weeks there can be a marked difference
Just an idea.....
Charlotte