SFO 1K has given you good advice. In addition, he should request wheelchair assistance for his connection.

Edited to add: I just re-read the original post, and see that your father would rather hobble than wait for wheelchair assistance. I agree with SFO 1K - it's a real risk.

That said, though, when I travel business class I do find that the crew will hold back the economy passengers to let me deplane first...