--I've never been able to find any material that's been publicly published that indicates difference in intraepidermal nerve fiber density norms by age and gender.

The original norming figures from Johns Hopkins' research did indicate a slight diminishing in the numbers with age but I haven't found all that much that is specific as to how much. Some other studies later on did not find significant diminishing of nerve fiber density with age, though. (This does seem to depend on what groups are chose for comparison. There is also some evidence of racial differences in nerve fiber density, though not all studies point that way.)

This first paper summarizes the norming figures on which the skin biopsy protocols are still based (it was published in 1998). Notice the means and standard deviations (which is to say that your thigh figures are below the average but well within the first standard deviation, by my calculation at about the thirtieth to thirty-third percentile):

http://www.ncbi.nlm.nih.gov/pubmed/9865794

This one, used by Aetna to provide indications for skin biopsy, summarizes a lot of other research since then (but by no means all):

http://www.aetna.com/cpb/medical/data/700_799/0774.html

Now, as regards the celiac testing, an elevated IgG anti-gliadin can be seen in a number of other autoimmune conditions; it is not as specific as the anti-gliadin IgA or especially the anti-transglutaminase IgA, which is the most closely associated with villious atrophy. However, those with gluten sensitivity often show with anti-gliadin IgG markers first. There is even some reports--mostly from Finland and England through the work of Dr. Hadjivassiliou--that those with isolated anti-gliadin IgG titres are more likely to show neurologic indications of gluten sensitivity,

You may know that much of the work on gluten-mediated neuropathy has come from Cornell and the work of Dr. Latov, Dr. Chin, and Dr. Peter Green at the Celiac Center of Cornell/Columbia/Presbyterian, building on the Johns' Hopkins' work.

One of the best places to read about all this is through the Gluten File that jccglutenfree (Cara) has put together. It is linkable right though our own celiac section here:

http://neurotalk.psychcentral.com/thread1872.html