use Unicode::Collate;
my $collator = Unicode::Collate::->new();

# first calculate the magic sort key for each text field, and cache it
for my $rec (@recs) {
    $rec->{SURNAME_key} = $collator->getSortKey( $rec->{SURNAME} );
} 

# now sort the records as before, but for the surname field,
# use the cached sort key instead
@srecs = sort {
    $b->{AGE}          <=>  $b->{AGE}
                      ||
    $a->{SURNAME_key}  cmp  $b->{SURNAME_key}
} @recs;