I agree with many of the individual factors he cited, but I think that quitting a job, especially a 6-figure job, after only 6 months is neither wise nor mature nor ethical, at least under the conditions he cited. It's not like it was an abusive situation or there was any significant dysfunction there. So I suspect he's on the young side. Bright maybe, but young.
That said, I'm not knocking his aspirations or desires.
In the context of traditional jobs, it's generally a good idea to stay at a job anywhere from 1-5 years, at minimum, before voluntarily quitting -- and this is speaking in general terms, because there is no perfect number, etc.
If you're laid off or fired, it's different. If the work situation is abusive or dysfunctional in some way, again, it's different. You have to show empathy also and look at it from an employer's point of view too: it takes a lot of effort to find somebody, especially find somebody good, and then there's ramp up time on both sides of the fence. As long as both parties make a good faith effort to make it a good situation, it's generally bad form for an employee to quit that early without significant mitigating circumstances in his life (family/health problems, etc.) Not saying you should stay there 10 years, that's too long in this field and economy.
Partly it's a judgement thing, and partly comes from perspective gained from past experience. If you ever want to work for somebody else again it will be a black mark against you in many employer's minds, for example -- again, without there being significant relevant negative circumstances at play. Also, unless you're a young adult, all of this would have been knowable at 0 months rather than waiting to the 6 month marker to realize them. So again, if you're a younger adult, it makes more sense and is more excusable. Been there, done that, have the metaphorical t-shirt. :)
That said, I'm not knocking his aspirations or desires.