I wouldn't either. I hope I didn't imply that. And the "grumpy old men" are just a stereotype I often see. My grandfather, for example, is the happiest (and wisest) man I know. But he isn't going to go start a company tomorrow that will revolutionise the way we communicate.
Can you really deny that the curiosity that children have is essential to society moving forward and staying youthful, and has to always be replenished?
Mental scar tissue is another issue too.
Maybe he won't do that because he thinks he doesn't have enough time left to properly grow such a company, to see it flourish and observe the impact it would have on the world? Maybe he doesn't have enough physical endurance and health to endure the challenges of being an enterpreneur? Or maybe his wisdom allows him to see that all of his ideas of 'revolutionizing the way we communicate' (assuming he ponders that problem) would not fare well if realized, and he didn't have the one that could work yet?
There are many possibilities here and the postulated lack of curiosity is just one of them.