Who entered in sololearn 1st Time in the world.??

Answer 1

probably the developers themselves in order to test the app

Answer 2

Yes. If you hack around you will see that user number one is 'Sololearn'.

Answer 3

The older user after 'Sololearn' who's account is still on as of March, 24th 2018 is 'andreng':

https://www.sololearn.com/Profile/4869/?ref=app

EDITED:

If you want to hack around too, change the number in the link.
For example, try changing it to number 1.