A bar whose primary clientele consists of older men, most of whom are married and go to an old man bar to get away from their wives. Most old man bars are spartanly furnished, and prices tend to be cheaper than average. There is a large overlap with "beer and shot" bars. Most old man bars are working class, as upper class men that age will congregate in country clubs or more upscale drinking establishments.
My unlce always goes to Jack's Tavern, but my aunt doesn't care because it's just an old man bar. He is not going to meet any women there.