The person being Bar Mitzvahed is going to be 13 years old. Good chance its not the person you think.
She she made the error I think its fair to ask if she is going to be gone in December because that directly affects you.
The rest of it is not your business and you'd be best to let it go.

ETA I just realized I misread the OPs relay of the initial text. It did say famous persons son
There is still a good chance it's not the same person though