Normally AGO is used in reference to the passage of time (three years ago, etc.). But sometimes, somewhat informally, people use it in reference to something else: Q: "How's Anne?" A:"Anne? That was four girlfriends ago. I'm dating Kathy now." Q: "How was Germany?" A: "That was two vacations ago. I just got back from Thailand." So, '300 million dollars ago' means at a point in the past before the most recent 300 million dollars were earned.

It's a play on words. Meaning that the person became a millionaire when he left college and made 300 million since then.