I do kind of like this idea, it makes it slightly more exciting, but a couple of things
my apologies first if they have already been covered, but i just thought i would post my thoughts anyway
ok, with the aptitude, maybe it could be like child to adult, for instance, you start out well, learning quickly, and as you progress through the game you learn slower, (though never to the extent of not learning or learning so slowly that there isn't any point, this would just cause character re-creation) that way everyone has the same chance at the start, and throughout, and then skills that you practice often, you would learn quicker than those that you rarely practice. for instance, if your a swordsman you can learn new sword skills quicker than say picking up an axe, or cooking the Sunday roast.
also, I don't think you should HAVE to have training you should pick up the skill without it, by practicing, but this would take longer than getting training on that skill maybe 70% slower without training. like in the real world, if someone shows you how to make a pot, you can go away and pick it up relatively easy, but if no one shows you, you can still pick up that skill, just first few times its going to end in spatters of clay all over the walls, but eventually you would pick it up.
overall though, i think it is a well thought out system.
Jay
