Technicaly that should be impossible.

Luke could be considered a true Jedi after dagobah.

Yet the story is 20 years later. from the start of the galactic empire. So Luke is 20 years old

Yet Luke became a Jedi Master at the age of 30

It than took him several years to take a apprentice. Than even more time to start the acadamy.

You could play that lord who worked with Dessan. But ,... Desan hasn't even been trained yet as a force user. 
I even doubt that the Vally of the jedi has been unlocked.