Check this suggestion for Retro/Disco party:
Have a COLOURFUL birthday party [less expense for guests and host]
The theme is bright and cheery colours. Everyone is invited to wear their most colourful outfit/make-up/hairstyle etc.
Lots of colourful streamers, tablecloths etc. Food dye [lightly administered] will colour food and drinks.
Play traditional party games - it is remarkable how you "grown-up" teen will revert to childhood if offered the right games to play.
Treasure hunting, pass the parcel, pin the nose-stud on the rock-star - take your pick....