Solved

Ovladač úroveň 30

You cannot buy drivers or staff that are a higher level than your team but you can train drivers to a higher level.

The Level 24 team with Level 30 drivers will have bought them at a lower level then trained them.

If you do this, you must be very careful not to let the driver contract expire, because you will be unable to buy them back until your team level reaches the same level as the driver you lost.

You can train all driver attributes up to 30. Personally I would focus on "Physical" first until BMI is green and Stamina attribute reaches 30.

After this I would switch training focus to "Driving Ability" until all trainable attributes (that is everything except Talent - which is not trainable) reach 30.

Finally switch focus to the "Mental" attributes and continue training until these are also maxed out.

Ideally you should initially employ a Talent 30 driver because Talent is not trainable so the driver will retain the same talent for their entire career.

Final note: As the driver LEVEL increases, the rate of training slows. Currently, when the driver level reaches the same as the team level the star rating will turn red and the rate at which the "Progress" bar increases will only be 3% each time you press the training button.

This answer is immediately before the much anticipated major upgrade, how (or indeed if) training will be affected by the update is yet to be seen.