The way Shepard described what he saw while talking to Anderson on the radio made it sound like Anderson was just way ahead of him in getting to the console. He mentions seeing areas that Anderson already talked about on his trek through the Citadel. Anderson charged in with everyone else, it was an all-out assault to get to the beam. I don't see why Anderson wouldn't have been charging too, though he's old and in command.

I had almost 100% war assets (only 50% galactic readiness because I didn't play MP), and completed every mission before the attack on Cerberus. The third option wasn't presented by the ghost boy, but I guess I could have walked into the beam anyway?