Baby False Map Turtle Concerns

Question
I found a False Map Turtle hatchling in June from the local river and am concerned because he has not grown at all since then. His shell also seems a bit flimsy and not as hard as I would expect it to be.I have not noticed any shedding either. I first had him in about a 10 gallon tank for a few weeks then transported him into a 40 or 50 gallon tank ever since. I read that it is best for turtles to have a UVB light and in the past few weeks have had a 13W lamp on him for about 12 hours per day. It is about 8 inches away from him when he is on his rocks. I offer him different types of food such as manufactured turtle pellets, carrots and other veggies, small pieces of cooked meat and the occasional fly I catch in the house. I feed him about every other day. His tank is in my kitchen with decent light from outside and is at the temperature of the rest of the house. I have not noticed any shedding since I caught him. There are no other animals living in the terrarium. I have never taken him to a vet. I have had pet turtles in the past (not this specific species though) and they grew. If you could tell me what I am doing wrong that would be great!

Answer
What you did wrong was to take him from the wild to begin with. There are far too many possibilities here, as he would be stressed being taken captive for one, you don't even know what temperatures of the water are secondly, nor did you mention a dry basking area and what those temps would be, nor what specific type of UVB lamp you are using, nor have you stated that you are using filtration in his water. The diet in no way other than the fly you mentioned resembles what he would receive in the wild, and certainly they don't eat cooked and processed meat, so this is a foreign diet to him. And a really quick way to kill an animal in a terrarium is to expose them to sunlight while they are in the terrarium. The soft shell frankly means low bone mineralization and this could be a precursor to metabolic bone disorder. My advice, if he makes it through winter, would be for release.