If that email is "very impressive", then I'm Jesus H. Christ. Any lepers need cured?
First, he's a bad writer. He'd barely get a C in a freshman English class, and that's with grade inflation. He doesn't know where to place commas or how to use punctuation. (That doesn't make his business emails unusual for the genre, but it rules out calling him "impressive".) Second, the only thing that is impressive or unusual (for that age) about his communication style is that, yes, he has an above-average level of confidence, and most 23-year-olds from middle-class backgrounds are still scared of their bosses, not talking about a business like they run the place. But who wouldn't have that confidence, after having so much handed to him?
This isn't damaging like his frat-boy communications but it's not really interesting. Sure, he knows some things about the business that he's the CEO of, but if he were 30 or 40 and wrote that email, people would be underwhelmed at his mediocrity, expecting better.
This bizarre age-curving is irritating because (a) what should really matter is where people are, and where they're headed, not whether they're 24 or 67 or 38+√(-163), and (b) because so much early success in the Valley is manufactured and delivered via connections rather than merit. (Silicon Valley's ageism is an expression of its classism.) Given that a 40-year-old CEO who wrote an email like that would (and rightfully) be considered somewhat off-the-ball, we should apply the same standard to Mr. Spiegel.