It's fairly new and hasn't gotten any bigger. He's not rubbing against anything like it's bothering me; I'm just concerned.
I've found this online but would still like to know more about it. I've never seen a turtle shed before and would like to know what to expect if this is truly the case.
Silvery spots under the top layer of shell
The silver spot is most likely air trapped under a scute that might
shed soon. (Not the whole scute to the bone, just one layer, which
turtles shed periodically.) Just keep an eye on it. Sometimes, the
spot turns green from algae that grow on it. You may try, gently,
to see whether to scutej (just a transparent layer) is loose and
comes off.

