I don't recall what year it was (perhaps 1997?), but Lucas stepped down as President of LucasArts and he's left those senior positions to others.
Lucas really is in charge of his Franchise Empire, but he let's others do a lot of the work, to leave the writing and directing of the prequels to himself.
From all I've read Yoda was always intended to be a little guy (just how little I don't know). But the early designs show him like a little dwarf, elf, troll, etc. type guy.