Attributes, Proficiencies and Skills.

Attributes:
Strength, Dexterity, Constitution, Intelligence ( + Charisma with social effects?)
These are slow in changing, and have a cap on both individual scores, and total score. (IE no single score may exceed 50, the total may not exceed 140).

Jamie has:
Strength 45, Dexterity 30, Constitution 50, Intelligence 10.
His training raises strength to 50, and he has hit the maximum.
Suddenly, his dexterity training has enabled him to increase his dexterity.
Jamie will be prompted to drop either strength or constitution by one.

Strength and Constitution are the two highest attributes not being raised at the moment (that being dexterity). Intelligence matters little to a fighter, so he might want to drop that, which is power play, but he can't. No warrior may ever approach 50 in 3 physical categories.

Attributes represent raw talent more than it represents development, although it may change throughout the game.

Minimum strength/dex for items doesn't work too well with this. I never really liked the system anyway. Such things easily bring my mind to Runescape. (Fun for 5 minutes) In this system, talent will help, but you should be able to build any character on these talents, by use of skills.

At any point during the game, you can set your 'focus' to one of the attributes, which you will be favouring in training. (Done offscreen, as it would be idle and unamusing for the player. I assume the character sleeps too. Mine has been wide awake for several days if only the healing bed rests count). The character must eat and drink during the day to gain the benefits of training. By training for (current attribute rating)/4 days straight (round up), the attribute is raised.

I've been able to do some thinking while writing.

Max rating (single attribute): 30
Max rating (total): 6 * 30 / 2 = 90
Starting total score: 4 * 30 / 2 = 60
Distribution of starting scores:
- All attributes start at values in the range 12 - 20.

There isn't much potential for growth, only specialization.
Attributes aid your actions. (And give more hit points, mana...)