Solved

Age Drivers

One of my drivers is aged a year compared to the other, but I took them both at 17 and they ran the same races. They have always scaled together. He is more stressed? :)

Primo arrivo had 1 more race, 184 for him and 183 for your other driver

But the age has changed always every 20 races

The age shown for a driver isn't their exact age, it might be something like 17.2 years old for one driver and 17.85 years old for another.