You’re right, Charlotte said not to begin school work until age 6, so you could easily drop MFW K. Sell it or save it to use when he’s 6.
I don’t do formal school for my kids until 6 generally either, because even if they are ready it’s a great way to burn them out early because developmentally they really just need free time and play, even if they CAN do formal school work.
If a child begs before age 6 I will do school with them (my 7th child is currently doing this) BUT the caveat is I only pull out school activities when they specifically ask me to. If they are too busy being little kids then I don’t pull anything out for them to do, period. This ensures they are the ones wanting to do the learning and that I’m not pushing.