What is weird that, the character doesn't develop when her/his skill become higher.
I think at least the height and weight can be increased/decreased according to the character's sex.
1. height and weight:
height can be improved a little bit, since the character started at age 16. Females can only stretch 1-3 cm, while males may continue to grow in early 20s.
For weight, it can either increase or decrease. Increase in weight will increase carrying capacity, and small animals/smaller humans find hard to compete her/him. Also fat in abdomen and forelegs (which females tend to accumulate) increase resistances to wound and cold. The bad is, the character become slower, and clumsy, also more likely to fail in some physical tasks.
I think height can affect speed (+ in plains, - in woods/caves), as well as the chance of physical tasks success/failure (depend on the tasks). Higher characters are more frightening and attractive.
2. Personality Stats
I heard in the wiki that the stats range in 0-18. So for intelligence, I think that it can be only increased by 1-2 in a character's lifetime (permanently, temporarily can be increased more by herb/drug) by practicing skills. Bigger fish like salmon or trout boosts growth.
Will can be increased to full as the character bother practicing, but also the growth is slow.
3. Physical Stats
Strength, Endurance, Dexterity, Agility, and Speed can be trained, but not to full (restriction of genetic factors...). There are sex/age bonus or penalties for that - for agility and speed, old characters and NPCs have penalties. Females are better in endurance while males tend to better in strength.
Eyesight, Hearing, Smell/Taste, Touch
They cannot be trained, only increase by "buffs". Eyesight and hearing will very slowly decrease in a character's lifetime (by 1-2 points) as character do more activities. For a elderly character/NPC, there is a sudden penalty.