As a person who loves turtles, I became involved in wildlife rescue for native box turtles.
It all started with a displaced box turtle who had her habitat destroyed by construction.
After doing a great deal of research, I began to learn so much about box turtles! Not that you only feed your turtle lettuce, but just because so many people are under the false presumption that lettuce is all turtles need, I just wanted to be sure you knew your turtle does not get much nutrition from lettuce.
Honestly, I hope you do not think I am being critical, I am not… Just noticed your turtle had some very dry skin and looked rather thin. You might try providing him with a reptile light and monitor the humidity level where you keep him.
I have found the turtles I work with do quite well with “Wardley Reptile Pellets” and a little sprinkle of “T-Rex 2:0 Calcium / NO Phosphorus”. I put the pellets in a little dish (about 2-3 tablespoons) and add twice as much water to the dish. I microwave the pellets for about 30-45 seconds and then let the pellets absorb the water, cool, then mash them up into a “mash”. The turtles love them! Every other day, I add mashed strawberries or chopped fresh mustard greens, collard, or carrot tops.