I did this for my 12th birthday and it was so fun! All you have to do is get everyone to dress up in 60's gear, which everyone can find in their attic or buy from charity shops for very little money. If they ask their parents, the costumes can be even more elaborate as they find their old favorite clothes! decorate with incense, candles and old posters/records displayed around the room. Get some old music together and everyone can dance, recreating a kind of old disco, play games involving music and if you have a camcorder, record a fashion show of everyone showing off their outfits. You can also play traditional party games and of course have loads of food and stuff including a big cake decorated with flowers, peace symbols, etc. With people aged 12+ you don't really need to plan any games as we are quite happy to sit around, talk and laugh at our clothes! This is so great, I repeated it and everyone enjoyed it just as much the 2nd time round, especially the parents as it brought back memories for them.