Sending CW with a paddle or any key is involved in intellectual centers of CNS and fine motor function. The fine tactile sensory function works as well when we touch the finger piece of the paddle at proper interval and pressure. Aging may have those functions deteriorated.
The following paper says passive sensory stimulation activates sensorimotor functions. They have done purely passive stimulations in the study, which is not thesame as keying movements. But I believe keying movements require fine discrimination of tactile sense that is comparable to these stimulations in a sense.
Old boys, don't complain of your clumsy fist but go on operating CW with a key. That will promise you to stay younger. I am telling this to myself everyday!
Clin Interv Aging. 2008;3(4):673-90.