A startup is company which doesnt have a stable cashflow and is searching for one. Thats about the only difference that really needs to be applied from a taxonomy point of view.
Impact is also completely unrelated to the label "startup". Private citizens, companies, NGOs, social communities and even projects-on-the-internet (eg: Linux) have had a huge impact on the world and its hard to say who has had more. Again another inane and useless conversation - who has more impact.
First make enough money to attempt to make an impact. Then you can try your hand at actually making an impact.