don't see many old sysadmins ... well, how many do you actually see anyway? Usually they're invisible. Secondly, the profession of sysadmin is disappearing fast with automation, and older and more experienced people have probably ridden that wave somewhere else already.
More precisely, "DevOps" is the new way to pretend we don't need a sysadmin. It usually doesn't take long for me to wish for a greybeard with a background in debugging kernel drivers.
