Thanks for all the great responses.  It really helps to know I’m not alone.  In my particular case, I was already starting to have some problems, perhaps mainly because I’m not 20 any more!  Then when I’m taking longer than I think I should to finish, it becomes a performance anxiety issue.  (As someone below said, I hate it when a girl says something like, “I want you to come for me now, baby!” – that shuts me down right away.)  Recently, I did start some new medication, and now climax is next to impossible.  No problem at all with desire and arousal, but the finish just isn’t there.  Sounds like the way to deal with it is to casually mention it up front, and not make a big deal out of it.  I suppose there is a bright side; if the girl’s up for it, I can certainly get my money’s worth out of the session!  It is frustrating, though, not to be able to ‘close the deal.’  Thanks again, folks.