Regarding being ready to found a startup, I'll fall back on the Justice Stewart's line that, "I know it when I see it".

When I was a young kid, I had an idea that I was going to have a plant store (really. I had just learned about splitting African violets) that would have 'low price days' and 'high price days'. I swear. They idea was that people would be so grateful for the low price days that they would go to the high price days to help keep the place in business. This would have been an idiotic company.

You ask when the authors of the blog post should have given up vs persevere? I would say either when the drew up the business plan or after the beta when the found that people didn't like their product and that they couldn't execute on their idea.

I'm unromantic on this point. To me a startup is to make money (as a profitable business or on the exit), not find creative outlet or have a life experience. I'd rather see 20-somethings blow the ~$5K spent on EC2 hosting apps with fundamentally broken business models instead on (AirBnB) trips through Europe or South America and getting a little bit interesting as people first.

It's up to them, but (to avenger123's point) almost nobody is a Jobs, a Zuckerberg, or a Musk. Most startups fail. Plenty of YC class startups fail, and they're the winners of a highly selective process with access to unbelievable connections.