I didnt know he was behind PayPal for example you see.His first company, PayPal, is worth $52 Billion.
His second company, Tesla, approached a $700 Billion dollar market valuation last year: before the short sellers attacked. The reason it did so is because the market generally believes it may end up replacing large segments of the auto industry if the rest of the industry refuses to react (which may also be who is now short-selling it so hard). Small though they are at the moment, even a conservative estimate of their growth indicates they may be about the size of Apple in 10 years: and that's assuming they don't consume the entire auto industry.
SpaceX is still private, but Google spent $900 Million for 7.5% of the company, giving it a rough valuation circa about a year ago of $12 Billion - they've made historic progress in the last year though: they're likely worth significantly more now.
So yea - by the time Elon Musk is old and grey, at this rate - he'll have all the monies. And a large swimming pool full of coins so he can Scrooge McDuck into them, built into his palatial pleasure-craft, in scenic low orbit over Venus.