foreach (sort keys %institution_table) {
    $institution_table{$_}{"fortyfive_fifty"} ++ 
        if  (45 < $age and $age <= 50);
    $institution_table{$_}{"fifty_fiftyfive"} ++ 
        if  (50 < $age and $age <= 55);
    $institution_table{$_}{"fiftyfive_sixty"} ++ 
        if  (55 < $age and $age <= 60);

    #...and so on up through the 85-90 age bracket
}