Giovanni
Yes, the maximum value was changed after last update. Now every stat can be improved up to 30.
First you have to improve stamina and BMI. I'm starting to not believe what anybody says about the green BMI. I have a theory about anorexic drivers because having less weight has a small advantage but I'm collecting data to support it. I start to think this because any academy driver is overweight unless is very short. I stop here my offtopic.
From my own tests I was able to prove that with a driver with green bmi was faster than a driver with red bmi that was 10kg lighter. Stats and height were equal.
This was only possible with legacy drivers though. I’m not sure if it’s possible for new academy drivers to be underweight instead of overweight?