Perhaps something like, make armor have both strength and agility requirements.
A character can wear all armor, however they get penalties if they don't have the stat requirements, relative to the level of the requirement compared to their own stat level.
So, if you have 3 agility and the armor requires 15, you have a very heavy penalty. However, if you have 18 agility and the armor requires 21, you get only a slight penalty. Same with strength.
With real combat you try to move into blows such that they strike more well protected areas, and do so in such a way that they glance off (or at least have, as M&B terms it, less of a speed bonus), so agility could be used to determine how well a character can use their armor's most well protected areas.
The way I would like to see this done would be:
-Too little strength would mean a movement penalty, as well as a slight penalty to how much protection the armor gives.
-Too little agility would mean a penalty to how much protection the armor gives and a small movement penalty.
Different armors would have different requirements depending on the type of armor.
For example, with full plate it really doesn't matter where you get hit, it's all plate, so the agility requirement would be very low, but it would have a higher strength requirement.
On the other hand armor like the Black Armor, or Lamellar Vests only provide partial protection, so they would have a higher agility requirement, but a lower strength requirement.