Any advice?

Okay so I’m 19 & my bf is 20 about to be 21 In 3 weeks, I want to spend the day with him for his birthday but I know his siblings and friends are going to want him to go out for his birthday ( to a bar, lounge) but the problem is I can’t go since I’m underage. It sucks that I can’t go and I feel like crap but than I also don’t want to stop him from going out with them for his birthday cause i know that’s unfair. He says he wants to see me on his birthday and spend the day with me but I feel like deep down he does want to go out and get drunk. I don’t want to stop him from going out but I know that day ima feel left out. And I also don’t want them to change their plans for him just because of me cause that’s selfish. What should I do?