Because you don't know which of the five years the employee will select to retire, and because they're getting into the range where it's not unreasonable to sup

Because you don't know which of the five years the employee will select to retire, and because they're getting into the range where it's not unreasonable to suppose that over a period of some years, they may need long leaves of absence to address medical conditions, etc. To be clear, I'm not justifying this attitude. Just explaining how it can be expensive to have older employees, even excluding potential impact on group insurance rates. Of course, on the flip side, you get a lot of benefits from a highly experienced, highly mature workforce.