I have also dodged the question about how long I nursed. I did nurse longer
than most of the moms that I see would even consider nursing.  (Nursed 3
babies, 26 months apart for 3 years 4 months, 4 years, 3 months and 3 years,
6 months respectively.)  I used to answer that they nursed until they weaned
me.  Lately my answer has been that I nursed them "much longer than is
culturally acceptable."  I find this feeds nicely into a discussion of why
we wean and when babies wean.  I really liked the article about a year ago
in BF Abstracts by the cultural anthropologist on comparative weaning ages.
After talking, if a mom pushes for the information, I will tell her honestly
how long each baby nursed.