Think you got a while yet, but it tells you if you need two drivers. If the car is good enough and he doesnt need to push hard then a level 0 driver in a 2 driver race should be fine, i used level 0 drivers in the level 25 endurance race and he was fine.
Extreme Series / European Championship (level 22)
I think thats the first event that needs 2 drivers.
Then
Endurance Series / Grand Valley 300km (Level 25)
That requires 4 drivers. (as do all but the 24hrs of LeMans Endurance races)
Many thanks.
rp2000