IMO, That is a narrow view. What is the goal here, start-up or business? If the goal is startup you may find that it never stops trying to start.
There are great established companies to work for and great startups to work for.
There are also terrible established companies to work for and terrible startups to work for.
I would also like to note that at good, established corporations there are two kinds of technical staff. The passionate kind with a decent mix of technical skills, business acumen and communication skills who work hard,are presented with interesting opportunities and are rewarded for their hard work, and the other kind who seam to always be complaining about the corporate environment and how it is holding them back. Often the "other kind" possesses adequate technical skills but has not taken the time to develop the business acumen and communication skills necessary to be proficient in a high-stakes business.
The first type will strive at any business whether established or start-up. The second type will likewise exhibit similar performance no matter the established date stamped on the business's letterhead.
Two good reasons, however, not too insightful (subjective).