What causes an elderly gentleman to show slowness of gait, bent over stature, confusion?

Most often. Parkinson's disease. But to be certain you should have him examined by a neurologist. A common finding is what is known as resting tremor, also called "pill rolling" tremor because the patients appear to be rolling a pill between thier thumbs and index fingers at rest, but when they reach for something, often the tremor disappears. There are other causes that any good general neurologist can ID.
DEMENTIA, PARKINSONS. But also a possibility of a condition called nph(normal pressure hydrocephalus) which is easily missed. Please discuss with his doctor.