this only works if event_age is a non-negative integer

I suppose they could be recording events that haven't happened yet and if they are then an additional flag for negativity fixes the problem.

my $raSortedEvents = [ @{ $raEvents }[
   map  { unpack q{x13N}, $_ }
   sort
   map  {
       pack( q{A8}, uc $raEvents->[ $_ ]->{ severity } )
       .
       (
          $raEvents->[ $_ ]->{ severity } eq q{OK}
          ? pack( q{cl>},
               $raEvents->[ $_ ]->{ event_age } < 0 ? 0 : 1,
               $raEvents->[ $_ ]->{ event_age } )
          : pack( q{c}, $raEvents->[ $_ ]->{ event_age } < 0 ? 1 : 0 )
            .
            ~ pack( q{l>}, $raEvents->[ $_ ]->{ event_age } )
       )
       .
       pack( q{N}, $_ );
   }
   0 .. $#{ $raEvents } ]
   ];
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Even more ew'ness I suppose but I did say this was over-complicated for the OP's problem and was just to illustrate a technique. It would perhaps look less dense if broken down into two stages.

my @sortOrder =
   map  { unpack q{x13N}, $_ }
   sort
   map  {
       pack( q{A8}, uc $raEvents->[ $_ ]->{ severity } )
       .
       (
          $raEvents->[ $_ ]->{ severity } eq q{OK}
          ? pack( q{cl>},
               $raEvents->[ $_ ]->{ event_age } < 0 ? 0 : 1,
               $raEvents->[ $_ ]->{ event_age } )
          : pack( q{c}, $raEvents->[ $_ ]->{ event_age } < 0 ? 1 : 0 )
            .
            ~ pack( q{l>}, $raEvents->[ $_ ]->{ event_age } )
       )
       .
       pack( q{N}, $_ );
   }
   0 .. $#{ $raEvents };
my $raSortedEvents = [ @{ $raEvents }[ @sortOrder ] ];
[download]