Riders training

Apologies if I make any mistakes here, trying to remember from memory.

Before the fall, do we actually know how long the apprenticeship would have been roughly? I.e start at 10 as a human then become a full rider at say 21 or 25? Obviously Eragon's was a abridged version, just curious thats all.

2nd part to that is I wonder what else would have been taught that Oromis had to skip