I would say that this piece is around grade 4-5 standard (depending on how well he wants to play it).
But thats still more than beginner standard!
I am actually in a similar position to you - I had a student book a lesson a couple of weeks ago and said to me that he wanted to learn a piece specifically so he could play it at his wedding. Not so bad, except that his wedding is in June.
So not only does he want to learn this piece, but he wants to perform it for his loved one, in front of all their guests, when he has never played the piano before.

Now I explained to him that we would start at the beginning and that I was in no way guaranteeing that I would have him ready to learn this piece by the time the wedding came round, but I would do my best and see what stage we got to in a couple of months before assessing whether it was really a possibility.
He agreed and we have had 2 lessons (he has already missed 2 others. hmm... ) where I try to teach him the basics, he plays it through (he is actually fairly talented and picks things up fast, which is lucky!) The after he's done an exercise once, twice at a push, he sits up straight, looks at me and goes "right, done that, next"!
I suddenly realised last lesson, that whilst he has agreed to learn from the beginning, he sees everything as something just to bang through, yep I've done that, so straight onto the next thing, like steps that will eventually get him to his piece. I know that learning an instrument is basically like that if you look at it, but am I missing something here?! Usually I want students to work on an exercise/skill until they do it
well, not until they just know how to do it - I think there is an important difference here.
What I'm saying, is that you may find yourself in a situation where he is learning everything in order to get to that piece he first brought up, and may never play it well. Now I guess for some people this is OK and they don't mind it, but I for one will am already uncomfortable with the idea that if my student manages to play his piece in time, he will in a way be representing my teaching skills, and I wouldn't ever want anyone to equate my standard of teaching with his standard of playing, if he is just going to bang it out ...