Idea's for a birthday party?!

You need to do something that caters to their age. Don't have a dora the explorer party lol.They are young adults so I would do like a theme based on what the birthday person likes. If its a girl do something like shopping related or make up...girly like. My cousin had a pink and black cake for her birthday that had shopping bags, shoes, and make up accessories on it. For game prizes you could give away nail kits, hair accessories, maybe gift cards to the local mall.

For guys, a good one could be a hawaiian luau with barbecue. Hold it later in the evening because if you have a fire pit, you can use it to make smores. Get torches too! they are cheap and make a dramatic difference. Also I think there are lots of people who spin fire torches. You can hire them to do a show.

hopefully those ideas help.