older,elder,都是old的比较级。但是两者是有区别的,elder表示前辈的、年级较长的,仅用于同一家庭成员的比较。例句:My younger son is five and my elder son is nine. elder在句中只作定语,不作表语。My elder sister does her homework all by herself.而older不限于同一家庭成员的比较,在句中既能作定语,又能做表语。