They may not have younger children at home, but they still have children/families (I live in an area where extended families tend to stay together, so that might be what's causing the confusion here), and they are more likely to have other family commitments than younger people. I also included other reasons why tech companies tend to hire younger people, because I don't think children are the only reason. It's mainly because younger people are generally more willing to work longer hours for less pay, for a multitude of reasons which include less familial responsibilities and less leverage for salary and workload negotiations.