SnapBird (www.snapbird.org) lets you find other people's Twitter messages posted much further back than what's archived in the results of Twitter search itself. You just need to know their Twitter username. For example, Glenn's handle is gutmach, so type that in the "Who?" field. Type your keyword(s) in the "For" field. Note that it searches within words for your string by default, so a query for ERE also delivers results containing there, wherever, severely, etc. So type it as " ERE" to avoid that (note the quotes and leading space)!