FileAge returns the modified time which might be changed by some user. Instead use
{$I %DATE%} and
{$I %TIME%}:
Caption := {$I %DATE%} + ' - ' + {$I %TIME%};
Note: that is the time/date the unit is compiled as, so if you have this inside a unit and that unit isn't changed for some time then the date/time will stay the same. So best collect that information inside the main program file cause that is compiled always.