How long should a steer live before slaughter?

That really depends on how that steer is being finished, what breed it is and how much meat (determined by size of the carcass) you want. There are different breeds that tend to reach carcass maturity a lot later than others, and how that particular steer is finished also affects the rate of finish that steer undergoes. For most steers in the feedlot, they are kept until they are around 18 to 22 months of age upon which time they are slaughtered. On grass, they wouldn't be slaughtered until they reach around 24 to 30 months of age. Steers that are very late maturing (like Jerseys, Holsteins, and Highlands), may not be slaughtered until they're at least 30 months old.