At the start of your characters life they often live, work, exist within the realms they belong. As such, certain classes and the relevant skills are understandably out of reach. Even those raised away from their homes may be still excluded from obtaining the required learning for perceived inability because of their race.
As any character may, upon reaching level 5 choose a second class and upon level 10 have the option of transforming one of those classes into an advanced one as a show of their evolution as a character from when they first arrived in Nathalion.
Many of these transformations would have been impossible if not for the things they learned along the way and the experiences they had. Many characters might have never seen a knight, shaman, or otherwise until coming to the melting pot of the city of which most of the roleplay is based.
As such, I believe that there should be some amount of consideration to allowing the races to learn classes not on their list after level 5 is achieved. While I think logically it could just happen as your second selection becomes available it could also be something you would have to prove via finding someone of that class to train your character, submitting the stories that lead them to the knowledge and or having all the same skill requirements for the transition.
This comes in line with the idea that the world around your character changes them.