Kareishu is a special smell that comes as old people age. Popular expressions such as: "Ossan kusai" or "Oyaji kusai" (smelly old man) refer to this smell.
加齢臭は、年を重ねると出てくる中高年独特のにおいのことだ。世間で言う「おっさん臭い」や「おやじ臭」というのは、この加齢臭のことだ。