A birthday party for adults can be fun to host. It's a reminder of a special person turning a year older. Over the hill theme is the most common for adult milestone birthday party. You can also consider some other themes like back to school party or forever young party.

In forever young party theme. You can decorate the room with health related posters like vitamins, exercise equiptments and some beauty products that claims to make you look younger. Request your guest to bring some beauty creams, lotion, or any health products. And of course, what goes with this theme is a healthy menu. You have to prepare vegetable, fruits and some othe healthy foods.

In Back to school theme party. Hold the party in school gym or hall. Don't forget to invite some old friends. Decorate the room with nice school colors, streamers, balloons and put your old year book on a corner table where your guest can see. Inform your guest that they should bring some of their favorite food when they were in school. It's so much fun to share and laugh remembering your younger years.

Food and Beverage
This will depend on what time and where your party will be. You should consider your theme. If you have a vacation theme. Then you can prepare nice fruit punch, barbeque, seafoods or some other food related to vacation. If just a simple party then you can prepare finger foods or some sweet treats. It's a good idea to know what your guest prefer to eat. Maybe some of your guest are vegetarians or they have health related problem that they cannot eat just any kind of food.

Invitations:
There are a lot of options in making your invitations. You can print out nice graphics that will match your theme from the computer or you can make some cut out projects. There are also different kinds of invitation card that you can buy at the store. You can even find one that matches your theme.
Another unique ideas is making a photocopy of your birth certificate and fill the back with your party information. You can also consider printing a baby picture and paste on a cardstock and put the details of your party inside. If your theme is vacation, then you can buy nice post cards use them as invitations.