It sounds like your turtle is ok, not huge, but probably not something you need to be too concerned with.

But, something I caught that could be bad for his longterm health; you said you feed him spinich. This stuff is ok in really small amounts but if it is a large part of his diet it can result in a ton of problems. The problem with spinich is that it "sucks" a lot of the calcium in the body out for whatever reason, so this could be one of the reasons why your guy is not as big as you'de like him to be. If you stop feeding him this that should be enough to fix it, and I would also dust with Rep-cal or whateve calcium supplement you use a little more frequently, just so you can catch him up to speed.
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