You want to replace c style for with list for?

Try this

   
my $min_diff_past = max (@all_date_diffs_past);
 
for my $arr ( @AoA_past ) { 
    if ($arr->[1]==$min_diff_past) {
        print $arr->[0]."\t"; 
    }
}
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(untested, you seem to confuse min and max)

NB: The foreach keyword is actually a synonym for the for keyword, so you can use either.