How to write 21st birthday wishes
A 21st birthday is a rite of passage in a lot of places, and the card usually gets read at the start of a very loud evening. Fun and cheeky works well here, especially from friends. Reference the night ahead, the group chat, or the stories you'll be telling for years.
Family can go a little more sentimental. Twenty-one is when a lot of parents realize their kid is really grown, so it's a lovely moment to say you're proud. If the person doesn't drink, skip the bar jokes and focus on freedom, adventure and the year ahead.