Cakes are usually associated with sweetness, especially among children. Kids love sweet things and that is why they always see a birthday or any special event as the time to enjoy. For your birthday cake, you could choose chocolate cake. Children and adult would love that. You could also prepare cake that is not too sweet in case of adult guests who are not too interested in sweet things or who are diabetic. Having this combination ensures that everyone has a nice time at your birthday party.
Bottom Line: When you're trying to come up with some birthday cake ideas, brainstorm! Make a list of what the person is most interested in, their likes and dislikes, the era of their birth, along with considering their profession, hobbies, and age as possibilities to help you create a that cake masterpiece.