二位数组的排序

$array = [
["name"=>"a","age"=>"10"],
["name"=>"b","age"=>"15"],
["name"=>"c","age"=>"9"],
["name"=>"d","age"=>"20"],
["name"=>"e","age"=>"50"],
["name"=>"f","age"=>"3"],
];
function asc_number_sort($x,$y){
if($x["age"]>$y["age"]){
return true;
}elseif($x["age"]<$y["age"]){
return false;
}else{
return 0;
}
}
usort($array,'asc_number_sort');
var_dump($array);