Assuming a go game takes 30 minutes on average, and you are never sleeping, resting, etc, you can do approx 18k games per year. In order to reach 4.9 million games you'd have to play for approx 280 years. So yeah, definitely not thousands of years :). Still, we are maybe one or two orders of magnitude away from the amount of games that humans need to play to become world class players.

That being said, the AlphaGo zero paper ends with the words:

> Humankind has accumulated Go knowledge from millions of games played over thousands of years, collectively distilled into patterns, proverbs and books. In the space of a few days, starting tabula rasa, AlphaGo Zero was able to rediscover much of this Go knowledge, as well as novel strategies that provide new insights into the oldest of games.