The problem is not that it gets harder to multi-task as we get older its the failure to accept that it is harder. Anecdotaly I would have to agree with the research. I have watched my parents age and am now watching my in-laws go through the same process and the issues are the same. Of course there will be variations between individuals but generally it is an accurate assessment. I once watched a Captain fixate on a slip of paper that should have been handed back to the groundstaff but the doors were closed and the stairs removed. By pressing the call bell three times to get someone to contact the flight crew he put the cabin on edge as three double chimes was also the emergency signal. Like I said anecdotal evidence but he wasn't the only older (over 60) Captain I saw do something similar. BTW I am rapidly approaching the same demographic and understand that my cognitive abilities are changing.