T.R.
My 9 year old son writes some of his numbers and letters different from the norm. It's anything that has a circle shape. a,d, 6,9, etc. His handwriting is very good, and is very readable. He is a smart, creative kid and does very well in school. I don't think anyone has ever commented on his particular way of starting his letters and numbers.
He taught himself to write when he was about 4 years old, and it has stuck by him ever since. But it is in no way, shape or form any big deal. If that is how how he wants to write-then more power to him!
My advise would be to let it go, and let him write how he feels compelled to write. Be happy that he doesn't feel the need to be like everyone else, and has his own way of doing things!