Depending on the beer, I'll finish a keg in one to two months...but, that's almost never entirely on my own. I share at least two or three growlers per keg, and during the warmer months will often have folks over for a post-work beer...although my spouse does help with some of the consumption, I am the main beer drinker in the house. I usually have three kegs on tap at once.
I've cut my beer consumption back a fair bit from where I was five or ten years ago. Most days, I'll have one (or none). On a relaxed Saturday afternoon, I might have a couple. But like BrewBama, I nowadays mostly brew lower alcohol beers (between 3.5% and 5.5% abv). I also have switched over to 12 oz. Willi Bechers for personal consumption, or 12 oz. tulip glasses...that way I can have the satisfaction of drinking a full glass but not a full 16 ounces! I also regularly have non-alcoholic beers on-hand, to switch things up if I want the experience of having a few beers but not all the alcohol/calories...there are some pretty passable options now beyond O'Douls. But that's for another thread!