I'd cash out at 23 for sure, because you never know when it's all going to come crumbling down. Look at Mark Cuban, who got rich on world.com (if you're think 'wtf is world.com', my point is clear), cashed out, and has a diversified business empire including cable tv and a basketball team. Not many people strike it big twice, or more.
The other key point is that being 23 and having $2.2 billion in the bank in no way prevents you from working, or doing anything else that you might happen to find fulfilling. It doesn't even necessarily prevent him from working for Yahoo. You can divest your stock holdings fully and still stick around and play with the big boys if you want. And of course, you have massive, massive freedom to set up any other kind of business you want. Look at the crazy number of ventures Paul Allen has been involved in, for example. Most of them were abject failures but his net worth kept rising with each MS stock-split anyway so who cares if you fuck up. He's having fun, he's employing people, stimulating the economy...
