Old man.

What do you think of the term "old man" to refer to one's father? Personally, it makes me cringe because I have only ever heard it used in a derogatory way, often thrown around out of anger and bitterness. To me, it speaks of a very high degree of disrespect for one's father. However, my son-in-law refers to his dad that way and they have a good relationship. When we asked him what he plans to have his own son call him, he said he would be fine with old man. So, I'm wondering if maybe it's cultural or generational or something else altogether. Until my son-in-law, I had never heard anyone use "old man" in a positive way. What do you think?