It sounds like your child is a self learner, so one thing to consider is that a computer can give your child the tools he needs to learn at his pace. My son has dysgraphia and couldn't write to save his life, but he could manipulate the mouse and keyboard, so it allowed him to work around the inability to write without slowing down what he wanted to learn. A computer is a tool, not a tv, so integrating it into his learning will not only mean he learns at his own pace but will also give the two of you some space. Gifted kids can be exhausting to keep up with, and if you're home schooling, you'll need individual time so that you don't burn out.
As to the writing, have you had him tested for a fine motor development delay or a neurological delay? If it is something other than asynchronous development, the sooner you know and start therapy, the better off he'll be.
