What are current statistics of readers of adventure travel books--age
range, sex, socieoeconomics groups?

Depends on what sub category of adventure travel book you are describing:

Adventure Travel books as guidebooks

or

Adventure Travel books as adventure novels

I don't know the demographic difference between the teo, but I am sure
that you want to differentiate between those that read adventure
travel books for fun and those that read them as guidebooks before or
while traveling.

Many sites, (though I only know only one, and it's currently in
development - www.adventure-travel-now.com ) offer adventure-specific
travel reads. I would contact a large travel publisher directly - like
Trvel and Leisure - directly. I am sure they could provide you with
demographics and statistics about the readers.