CI can last a century, galvanized from 1953 could be worn out, or still fine - depends on where in the system it is. If it is a vent, it might still be fine. If it is a drain line, it could be all plugged up with rust. You'd need to be on-site to determine which.
Keep in mind that CI damps noises much better than the plastic replacements of pvc or abs, so that is an issue as well. CI costs more than the plastic, but if you go with the hubless version, you won't need to learn how to lead a joint.