He is a confirmed Goliath. Note the red tail bottom and such. I know because he was shipped directly and purchased for me by the owner, I am building a 1000gallon tank for him when he grows up and for my Alligator gar, Armatus and such.
I would recommend starting around 4-6in, starting at 10 can be a bit overwhelming, also if you plan on putting him with anything else and get him at 10in then everything else best be at least 14inches.