Nick
New drivers reach a maximum rating of 18 even with all traits maxed out, instead of 20 like it was long time ago.
You can get a driver up to level 20 if you train everything up except one attribute, if that driver then reaches 20 experience and you train the last attribute to 20, should give you a level 20 driver.
That beeing said, the level 20 driver will have no pace advantage over a fully trained level 18 driver, it’s just a cosmetic thing