How fast does a box turtle grow?

I've had this box turtle for about 15 years now and he has stayed about the same size, then I got him a terrarium that is 6ft long and started feeding him healthy turtle food from the pet store on a daily basis and I swear he has grown a lot in the past 2-3 weeks. It is hard for me to tell, but he looks huge... show more I've had this box turtle for about 15 years now and he has stayed about the same size, then I got him a terrarium that is 6ft long and started feeding him healthy turtle food from the pet store on a daily basis and I swear he has grown a lot in the past 2-3 weeks. It is hard for me to tell, but he looks huge compared to before. I swear his shell must be an additional 1/4 inch longer than just a few weeks ago. Could this be possible? Do turtles really grow that fast? His shell was about 4 1/2 inches long a few months ago when I last checked and It seems to be closing in on 5 full inches now. Is this just him being fat from eating so much? His body seems bigger and his neck seems longer too. He is also very active and energetic. How big do these things normally get? I don't want him to be 12 inches long in a year lol.
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