Since your boyfriend is a rich second-generation, he must have everything he needs, and all he eats, wears, and uses are branded. You can directly ask him what he likes and give it to him on his birthday. Maybe he will take it to heart. Here are a few small suggestions:
1. Since he is your boyfriend, no matter what your family gives you, it is always inferior to the things given by the person you like. As long as he likes you, he will treat the things you give as treasures and will not dislike the things you buy for being low-grade. So you can choose a gift based on his preferences with confidence, and you can choose a gift that you think is suitable for his personality and temperament. I believe he will be happy to accept it.
2. You can also not give anything, but make something for him personally, which will be more meaningful. Let him know that you have him in your heart, and he will be very happy.
3. You can personally make a candlelight dinner and decorate your room, and celebrate your birthday together. I believe he will be very touched.