sorry to disappoint you on the crowd at SPT. The crowd that hangsout late at the lobby/bar/casino around the hotel are not the 20 something crowd. For 20 something crowd hangout you are better off going to Covent Garden or Queensway.

OT: if you are spending two days in London I would recommend getting the two-day day pass if u'r planning on using the train/bus/underground. The Oyster card is more convenient to use but only if u'r planning on using only the bus and underground. Have fun in London. It is one of my favorite places as of now Check the weather before you head out as the London eye experience is a must only for a sunny clear-day in London. cheers!