Startup founder and CEO here. My startup is still a real one, young, small, and not secured at all. Not funded, we are 100% bootstrapped. No doubt it's a startup. But one day, maybe it would be hard for me to say I'm a CEO of a "real company", which is not a startup anymore. I think I won't do that. And it will not be an excuse for anything you may think about.
In fact, being CEO in a startup is a very different job than being a CEO in an established company. Being a CEO is not my goal. I wouldn't like this job. I'm not attracted by power or titles. I like money but to a limited point which is easy enough to reach without being CEO or founder. What I like is innovation. Being the visionary guy in an innovative startup. That's why I'm a startup CEO.
What will be the future for me ? If my startup is a large success, I won't be the CEO of the established company. Maybe I could become CTO or VP in a big company after M&A. Or maybe I could hire a "real CEO" and become CTO in my own company if it grows independently. Or maybe I could retire and write books...
If my startup is a modest success, it would mean it became a small business. I'm Ok with the title of "business owner". That's fine as soon as I'm free to imagine, create and deliver innovative products. After all, there is not much difference between a bootstrapped startup and a small business, if you reason in pure financing terms. But I think I will use the word "startup" as long as I will produce risky innovation with fragile financing. I like this life, and I like the word which describes it.