They used to be unlimited, but a cap was put in place because the devs don’t like anyone getting over 10. You need to find creatures with higher melee/dodge skills to be able to get experience, and since most creatures in the game have <10 you end up getting incredibly low amounts of exp for your melee skills. Try fighting things in the mines, or letting soldier ants attack you for a few days and you can get dodge higher than 15 if you try. Melee itself is far harder as you kill your exp sources.
Ranged weaponry is capped based on dispersion of the weapons, which have a hardcoded minimum, so those seem to stop around 17 or so, though with effort you can get them a bit higher.
The goal of the devs was that 10 is supposed to be the maximum, but some skills can get around that due to their nature of being incredibly commonly used (mechanics, survival, driving) while others just get more experience due to larger values, leading to a higher cap.