long in the tooth
年龄太大，已经不再幼稚或有活力的
口语·形容人或物年老
英文释义
old or aged
例句
My dog is getting long in the tooth, but he still loves to play fetch every morning.
典故来源
源自马匹年龄判断：马年纪越大，牙龈萎缩，牙齿显得更长。