This requires at least a 35 Medicine skill. Once your character gains access to the main strip, find Victor outside the Lucky 38 casino. He will tell you that Mr. House wants to meet you. Follow him inside and go up the elevator. Speak with Mr. House (the giant television face that looks like Howard Hughes). Find the dialogue choice pertaining to needing to ask him a few questions. Then, ask "Who exactly are you, Mr. House?", then select "You appear to be a computer, not a man". After that, select the Medicine skill check response, "The lifespan you're claiming is impossible, except for ghouls and super mutants." After that, you will be awarded 35 experience points (or 39 experience points if you have the Swift Learner perk). You can repeat this as many times as desired.