There’s no universal agreed upon definition for a startup but if at all you want to think of one, use growth rate. They have 1000 employees and $1b in the bank now. They had 1000 employees and $500m 48 hours back. They had 500 employees and $250m a year ago. They had 250 employees and $100m 2 years ago and so on..

No “non-startup” can grow at that pace.