My answer to "is he ready" is always a firm and clear "YES."
When parents ask such "ready" question, I know they have a big doubt about their child's ability. The doubt is so large that it often prevent them from taking any action. Several weeks or months have passed, and the student still has not played in any tournament.
When a baby tries to walk, do you ask such a question: is he ready? When the baby falls down, do you stop him from trying again right away?
When you send your baby to daycare, do you ask: is he ready?
When you send your baby to kindergarten, do you ask: is he ready? can he talk to the teacher if he needs to go to bathroom?
NO, you never ask such questions. You just do it, and handle any issues that might come up later.
Tournament is a fancy name for non-casual play. Yes, there are a few rules: touch move, no talking, etc. Your child has gone to the chess club, has come to my chess classes, and has played chess games for several months now, so s/he can play in tournaments too.
If I organize an internal tournament in classroom one day, do you have a chance to ask "is he ready?" No, you don't. Will your child play? Yes, s/he will.
So don't ask, just do it!