When is a startup not a startup?

Startup news: Zoopla wins "Most promising European tech startup of 2013".

A startup? Zoopla? It's been launched for nearly 6 years. Turns over something north of £30m, spent millions on acquisitions, been through a merger, employs 100s of people, and has £10m cash in the bank.

A "start" up? It's a bit like "New town" Linford, which is now the best part of a 1000 years old. Surely there's a point at which a startup stops starting up and becomes a company, some combination of factors, a line in the sand, that means you've passed the startup phase.

A length of time in the market place; should that not be relevant to the definition of a startup? Or is it only after a long time (by company standards), e.g. 10+ years? Google is 15, Facebook is only 8. Can't call them startups, surely?

Does how big your company has become not have a bearing on your status as a startup? Revenue, numbers of employees, something? The UK average company turnover isn't much over £500k. Ignoring one person companies, the average company employs 15 people. So exceeding the average by more than an order of magnitude doesn't disqualify you from being a startup?

Nothing about the stages you've been through? Acquiring other companies, going through a merger - these seem like the actions of an established company, not a startup. But maybe that's not included in the measure either.

Ahh, wait. Is the only thing that disqualifies a company from being a startup an exit event? So the company has to be acquired or go through an IPO. Which would suggest that the concept of a startup is being defined by the interests of the investment community rather than, say, anyone else.

Given the passion that drives people that start up a business, that's a bit sad, isn't it?