well, i dont think to much time. this is my theory.
the keyblade war took place, all keyblade wielders died in the war (this is confirmed by MX at the end of TGS TRAILER 2009).. exept MX and ME.... so they have to look for new posible wielders, and this is when TAV apeard and BBS takes places.... dont know how much time exacly.. but no more than 5 years.. (most liky less)
thats why theres almost no keyblades wielders anymore.......
with the battle between MX, vanitas, ME, TAV and king mikey(bbs plot), the keyblade wielders disapeard.... and they re-apeard with sora, kiku and the king again....(kh 1 plot)
seems like a scratchy generalized theory that can only be supported by (and Im not cocky) my theory in the thread. But still yours is too loose as you put too much of your opinions to it.