Here's a chance to let your guests relive (or remake!) their teen years: Invite them to a night at the prom.
Prom night is best done big, so you'll want to find a venue that can accommodate half a dozen round tables (or more, depending on the size of the guest list) and affords a large dance floor. Decorate with lots of strung lights, balloons and flowers, and to do it right, you'll want to hire a band, so a real stage will add to the event. An outdoor nighttime setting is ideal.
In your invitations, make it clear the prom is formal attire. Include a message asking each guest to send you photos of them at their original proms in advance of the event. You can hang these on walls or place them in stand-up frames on tables around the periphery. Guests can get to know each other while sharing their original prom stories.
Whether buffet or sit-down, you may want to hire a caterer; or if you decide to cook the meal yourself, you'll still likely need wait staff to cater to the evening's happy prom kings and queens.