A couple of things. First off, I would seriously doubt that the dragon are CBB so the pet store would have no clue as to how old it is. A few people have bred them, or more specifically a few people have successfully hatched eggs from a WC female so I suppose there is a slim chance that the babies were at least CH and the store knows the age. I wouldn't put any money on it though.
Second, I know that the temps for incubation are lower than one might think. 70 is not to low as far as I know.
Check out this site.
http://www.froggieb.com/MHDHome.html
Marcia was the first, or at least one of the first, to breed these animals and publish the results.
You should be able to find what you need there.