PHP implements querying the data matching the date of birth according to the entered age

Requirements describe ： The front end sends requests such as 33-55 year , After getting the age data, the backend converts the specified age into date

$search = $_POST;
$year = date('Y');
$month = date('m');
$day = date('d');
$max_birth = '';
$min_birth = '';
//  The user entered the minimum age and maximum age 
if(isset($search['person_age_min']) && isset($search['person_age_max'])){
    $min = min($search['person_age_min'], $search['person_age_max']);
    $max = max($search['person_age_min'], $search['person_age_max']);
    #  Calculate the earliest date of birth for the maximum age 
    $max_year = $year - $max - 1;
    $max_birth = date('Y-m-d', strtotime("+1 day", strtotime($max_year.'-'.$month.'-'.$day)));
    #  Calculate the last date of birth for the minimum age 
    $min_year = $year-$min;
    $min_birth = $min_year.'-'.$month.'-'.$day;
}elseif(isset($search['person_age_min'])  && !isset($search['person_age_max'])){ // The user only entered the minimum age 
    #  Calculate the earliest date of birth for the maximum age 
    $max_year = $year - $search['person_age_min'] - 1;
    $max_birth = date('Y-m-d', strtotime("+1 day", strtotime($max_year.'-'.$month.'-'.$day)));
    #  Calculate the last date of birth for the minimum age 
    $min_year = $year-$search['person_age_min'];
    $min_birth = $min_year.'-'.$month.'-'.$day;
}elseif(!isset($search['person_age_min'])  && isset($search['person_age_max'])) { //  The user only entered the maximum age 
    #  Calculate the earliest date of birth for the maximum age 
    $max_year = $year - $search['person_age_max'] - 1;
    $max_birth = date('Y-m-d', strtotime("+1 day", strtotime($max_year.'-'.$month.'-'.$day)));
    #  Calculate the last date of birth for the minimum age 
    $min_year = $year-$search['person_age_min'];
    $min_birth = $min_year.'-'.$month.'-'.$day;
}
if(!empty($min_birth) && !empty($max_birth)){
    // sql sentence 
    $sql = "select * from user where birth between $max_birth and $min_birth";
    
}