What if the adult has a nickname? You can mention/reveal his real name (he has to show id, people in authority/family members call him Jude while others call him something else). It could be obvious that his name is Jude, and also make it more clear who's being referred to. Additionally, nicknames usually have a story behind them, and can help reinforce that he's a person with a life and a history and interactions with others. Even if people just refer to him as J or Jay.