young fogey

A young person who acts older than they are, due to conservative and/or outdated beliefs and behaviors. A play on the more common phrase "old fogey"—and older person with outdated ideals. Primarily heard in UK. You don't want to come to the club? Ah, you're such a young fogey. I can't believe you're going to bed early on a Saturday night so that you can go to church in the morning—you're such a young fogey!