Perhaps he ahs parkinsons or a related neuro issue? I have a friend with parkinsons. He gets stuck on occasion, its no big deal. Also Michael Fox did a season on Larry David and made fun/educated about this symptom.
Transient ischemic attacks are also not uncommon among the elderly (aka "mini strokes"). But Parkinson's is hugely common among old men, in particular, and doesn't have to mean there are any cognitive issues.