First and foremost, it's perfectly reasonable to feel nervous about this conversation. It's always difficult to anticipate what someone else might be wanting to discuss, especially when it involves your loved ones. However, it's important to approach this conversation with an open mind and a willingness to listen.
It's possible that your daughter's boyfriend could be asking for her hand in marriage, but it's also possible that the conversation could be about something else entirely. Perhaps he wants to talk to you about his plans for college or his future aspirations. It could be that he wants to discuss something going on in his own life that he would like some guidance or advice on.
Either way, it's important to approach the conversation with kindness and curiosity, rather than immediately jumping to conclusions or shutting him down. Listening to what he has to say with an open heart and mind can help you better understand where he's coming from and what his intentions may be.
If he does in fact ask for your daughter's hand in marriage, it's important to take some time to think things through before giving an answer. While 18 may seem young to some, it is legal age of marriage in many countries. Discussing this decision with your daughter and understanding her own goals and aspirations is important. You may also want to involve a trusted family member or friend in the discussion to provide additional support. Ultimately, you and your daughter know what is best for your family, and you should do what feels right for all of you.