I guess 23, when I moved out for the first time. I didn't have much money, and I didn't really buy any furniture, but my room-mate and I certainly made the place our own with our (and friend's) artwork and thrift store finds. I was 31 when I bought my first real piece of furniture--a futon and frame, It was also my first place alone (with no room-mates).
How old were you when you first lived with a romantic partner?