You must take into account his age when making the decision.

take 是动词，意思是"采取、拿取"。 into 是介词，表示"进入...状态"或"转变为..."。 account 是名词，意思是"考虑、计算"。 take into account 是一个固定短语，意思是"把...考虑在内"，指在做决定或判断时需要将某个因素纳入考量范围。