50 years is a lot of time to remember. Things happen, so celebrate the past as your 50th birthday party idea. Get pictures of the person's life throughout those fifty years. The music that was popular when the person was in high school or college, and have food that was popular at that time. Party games can include "Guess What This Is," where a special item is shown to the guests and they try to guess what the item is and why it is so special to the birthday person (who must, of course, tell the true story for each thing after the guessing is through).
50 is an age of maturity. Go for a sophisticated type of party. Quiet, classical music with 3 or 4 great wines, half a dozen of great cheeses, and some fancy crackers. Have classic decorations with linen tablecloths and napkins, fancy crystal, china, and silver on the table. No games but a polite toast to the birthday person. If you have party favors, include miniature bottles of wine or liqueur.
Have your guests come dressed in costumes of a certain era. Serve food of that era and include music and games of that era also. Get your guests to dance period dances like the minuet at this 50th birthday party idea.
A pajama party is a great 50th birthday party idea!! Have guests come in their nicest nightwear, and plan for the birthday person's favorite movies and party games. Make it an all-nighter by providing futons or air beds for guests to "crash" on and don't forget the popcorn!!