The people my age that suffer career losses and anxiety usually do so because they stayed in one place too long. Getting laid off or fired after 10-15 years (or longer) in one place can be disastrous. Part of it is that they no longer have practical interview skills, or even understand the current trends in recruiting and hiring. But a lot of it is because their skill set becomes company-specific, deeply tied to the business of their long-time employer. They might be (and often are) fine programmers or analysts, but their resume doesn't reflect that.
As for startups... if you think an initial product (MVP) having bugs or lacking features is the reason startups die, you're not paying much attention. I would go far in the other direction! A company that doesn't release a buggy, incomplete product will die. That's because startups are a race against the clock. They need to show results (usually measured in sales) quickly enough to not run out of money, or at least get them to another round of investment to keep them going. The longer the time to market, the harder that is. And customer feedback is the best way to find the shortcomings in your product.
The reason anyone buys from a startup is desperation. That startup needs to be offering something that cannot be obtained from an existing, stable market player. This is especially true in B2B, where businesses are actually risking something by committing to a startup, other than their free time. A startup needs to find such a big pain point, such a big market gap, that customers will put up with a buggy, incomplete app, and pay for the privilege. That is the secret to a successful startup - certainly not polishing the turd til it glows. (Read Crossing the Chasm for great depth on this, if you don't mind a bunch of boring soft-skill reading.)