Thank you for all the replies. Yes, she is listed as an herp vet and sees lots of turtles.
BoxTurtleLover, how old would you guess they are (there are two of them)? And what should I expect in terms of life span? They had been without UV light for a number of years when I got them. Her beak is deformed (doesn't align) and they feel she may have had metabolic bone disease. Her color hasn't changed and he has gotten much brighter and more handsome. They both gained a little weight and have maintained consistent weights for the past year.
Both were treated on antibiotics when I got them and he was treated again last winter for a respiratory infection. I am working at keeping the habitat more humid this winter and getting the UV light down closer to them. Practice, practice....I'm still learning.
In response to your questions above, one can only estimate the age of a box turtle unless one hatched it out of the egg itself or knows the person who hatched it. Otherwise, box turtles, due to genetics, environment and diet, all grow at different rates and different sizes. An adult is impossible to age (again, as above as to hatching), and one can only guess. Turtles way up in age almost always have very smooth shells and some older females, possibly due to years of egg laying, may have thin, baggy skin hanging out of their hind leg area. All I can say is your turtles are definately adults and if in captivity 25 years when obtained and an adult at that time, you can safely say the turtle is any age over age 30, but due to the smoother shell, could be pushing 40 or higher. Hard to say.
The lifespan of box turtles in the wild and in captivity varies with all sorts of factors also as some people have them in captivity for well over 40 years acquired as an adult. As long as you give your turtles a proper environment and diet and good care, they should have many years left with you.