Why can’t Protestants that believe in the true presence of Jesus in the Eucharist receive it?

I’m asking for one of my friends who is a Protestant and is likely to convert. I’d love for him to be able to receive the Eucharist because he already believes in the full presence of Jesus in it, but I’m afraid telling him that he has to be confirmed first will be off-putting. Simply because if you believe that it is truly Jesus, isn’t that all that matters?

I know it’s a different story if it’s a Protestant who doesn’t believe in try Eucharist. But for a converting Protestant or one thinking of converting, why can’t they receive it?