Took my daughter when she was 15 and again at 18 to vegas- had a blast both times, we stayed 4 days one trip and 3 the other. One day we did a pink jeep tour to the hoover damn and grand canyon, the rest just things on the strip, shows, looking at all the hotels and what they have to offer, rides etc. Washington DC we also went to- it was just "ok" neither of us were overly excited about it and the area surrounding DC is trash. I dont think I would want to spend 4 days there.