下面是一个自己写的根据出生时间计算年龄的方法

function birthday($birthday){ 
 $age = strtotime($birthday); 
 if($age === false){ 
  return false; 
 } 
 list($y1,$m1,$d1) = explode("-",date("Y-m-d",$age)); 
 $now = strtotime("now"); 
 list($y2,$m2,$d2) = explode("-",date("Y-m-d",$now)); 
 $age = $y2 - $y1; 
 if((int)($m2.$d2) < (int)($m1.$d1)) 
  $age -= 1; 
 return $age; 
}