Agree totally; everybody from the captain to the receptionist has potential to screw up and affect somebody's safety. I just see absolutely no reason for anybody in an aviation working environment, to be above the 20%mg level that applies to aircrew.
Also, if anybody troubles to read the research, it's ability to make decisions and consistently follow procedures over a period of time that degrades first, manual dexterity much later. Strangely enough, what are Engineers doing? - following procedures and making decisions.
G