All I'm going to say right now is that if you watch EMPIRE, Yoda's refusal to train Luke because he's "too old" is more than comic relief. It's not just Yoda not wanting to train Luke. Psychologically, it is realistic, because he is afraid of the mental toll it will take on the young man. His real concern is that Luke will not finish what he began. God damn, the line sells Yoda as a caring, sympathetic wise "man." You even see in Luke's face that he knows Yoda will give in, and that he appreciates the thought behind the effort. Lucas would never have got this sort of a moment out of anyone on any of his own films.
Lucas didn't understand this, of course, since he didn't write EMPIRE. It's been said a bunch of times here already, but using that line as the basis of anything dogmatic and serious pretty much tore its EMPIRE usefulness all to shit. TPM returned the line simply as a factor in the whole JEDI training process, in one swoop erasing all of Yoda's humanity.
LKMCMITN.
PS:
Okay, one more thing. Yes, Mac, it's common to nitpick the movies you don't like and forgive the ones you do like. The common thread here is that a lot of people were disappointed with JEDI, because it wrapped things up rather sloppily, thank you. So its other shortcomings, especially its ROAD TO MOROCCO humour, stood out like a Wookiee at a Klan meeting.