When they stop asking for free money.

When it no longer relies on investor capital to fuel its operations and is able to fund its self and its growth through its own profits.

I think the looser definition is once you finish rapid scaling up. Like some people controversially considered Tesla a startup for so long even though it was a huge organization that had been around for years and had a huge market cap, because they were still “scaling up” by building lots of factories to be able to rapidly increase production and weren’t technically profitable sense they were reinvesting all their money back into expensive factories.

I don’t think Stripe and Bytedance should be on the list as they’ve more or less finished growing and are self sustaining profitable entities

I guess when they don't want money from investors.