Hi - I know there are others here with experience in this specific matter, and so I preface this with saying this is only my humble opinion. Since he is only 5, and ND kids are also just learning to write at that age, perhaps you can introduce the keyboard for all his learning activities he loves, and then just have a very short daily writing practice?
Hi, I just wanted to add: where I live (Netherlands) children start learning to write at 6. Any Dutch would tell you 'of course, he is too young to write anyway'.
This is as well just my humble opinion though...