What does this professor mean by saying "I do not have time to respond" I am an undergraduate in CS and engineering.  Approximately a week ago, I sent an email to a professor whose research really interests me.  I sent him couple of my questions and confusions rooted from reading his recent papers, but I did not get any response.  Consequently, I sent a short followup email to him indicating that email was sent a week ago, but he sent a short reply saying that "Sorry, I do not have time to respond."  

Does it mean that he wants me to go away and never bother him again?  Does he not like me (we had some previous but positive communications) or not want to be bothered by undergraduates?  Should I perhaps send a followup email a month later?
Keep in mind a very simple rule: Professors are human beings

Many of the questions on this site seem to assume from the outset that faculty are strange, mysterious and mercurial creatures, whose motives are entirely opaque and whose every word must be subjected to an intense amount of kremlinology.

"Sorry, I do not have time to respond." means that he doesn't have time to respond.

There could be many reasons for this. He might be particularly busy at the moment - lots of conferences take place in the summer, and many academics also use it to catch up on work not done during the academic year. If he is, as you say, approaching emeritus status he may be occupied with wrapping up things he's intending to walk away from. He might be dealing with other things in his life.

You should take that message at face value, and try not to impute any sort of hidden motive onto it - you simply don't know enough to know. Try following up in a month or two with a simple question as to whether or not his schedule has freed up and he might have some time. If the answer is still no, let it go.