What about startups that get a second wind?
Companies do get a second wind and come again, sometimes with a new technology; more often with the same technology re-applied to the latest technical and business conditions; some times with the same technology and a new business model.
Also relevant timescales are different in various industry sectors. An EDA company should be able to get going and show – or fail to show – success much faster than a company working with deepest darkest sub-nanometer physics.
Also, startups are often "stealthy" for a couple of years before they start to talk about their tilt at the market so I tend to think of those two years plus another two, three, or four years as their window of opportunity. Of course, there are some circumstances where engineers form a company, go away and do something else – design services for example – and only later start to develop their business. So you end up with a company with X years of existence but only Y years of endeavor. So it becomes complicated.
There are no hard and fast rules but I still think it is hard to class a ten-year old company as a startup.
A ten-year old startup phase might make sense if we knew a company or its technology was going to maintain it ssignificance for decades to come. But of course we don't know that.
I would argue that a ten year old loss-making, privately-held company sustained by investment or that has found new investment, would be well described as a privately-held company with aspirations and backers.
But what do you think?
Related links and articles:
EE Times' Silicon 60
GloFo runs with Adapteva, Cyclos IP
Cadence buys analog IP startup