All of them were used when I got them with the exception of one that I built.
Normally about 3 to 4 years, then I usually take them apart, save what I might need & scrap the rest.
Picked a 1 to 2 year old machine from the neighbors scrap pile last fall, gave it to mom after I cleaned a ton of adware off of the hard drive. Amazing how many people will invest in a good setup then run it with expired security or none at all...then set them out curbside when it starts to screw up.