Why it is not accepted: "Jsi ty velký kluk"?
That is a question word order.
I don't understand your statement
The proposed word order is good for a question, not for a declarative sentence.
Is it a different meaning when you say "hoch" rather then "kluk"?
I don't understand why "ty jsi velký kluk" is not accepted. "ty" means you...
"Ty jsi velký kluk" is accepted. But we have no report for it, so we can't tell you why what you wrote was rejected. Please use the Report button, if you're reasonably sure that your answer is correct, even if you also comment.