Other mistake: When Dixie and Mr. Hart are on the elevator, we see the number five lit up on the panel above the door as they head down to the first floor in the ER, where they meet Johnny and the kids, who get on the elevator to head up to the fourth floor. The problem is that the ER is only a 2-storey building.
Other mistake: All the guys are sitting around the table in the day room discussing how smart kids are, and when the tones drop we hear the dispatcher say, "Squad 51 possible assault victim," yet all the guys from the engine company rush off and head to the rig in the apparatus bay, even though only Roy and John were called.
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.