Propinquity - S3-E20
Other mistake: When Station 51 is dispatched to the traffic accident, while en route first we see Engine 51 with nobody on the back, but then we see two firemen standing at the back, and they are Johnny and Roy. This footage is from the episode "The Old Engine" in season 3, when Station 51 got the new Ward La France engine, and since the previous shift was still out with the squad, Cap told Roy and Johnny to jump on the back and join them on their first run with the new engine.
Answer: I believe you are speaking of the old man, Mr. Wilson. He's played by J. Pat O'Malley.
Bishop73
Correct, it was J. Pat O'Malley...he also played the grandfather with his grandson when their rocket exploded, and also played "Old Bill" in the episode with Ann Prentiss, where Gage saves the little girl from the burning tree house, and her mother falls in love with him.