Early reading can be common in gifted children, however, not all gifted children are early readers (my son is PG, and not an early reader), and not all early readers are gifted.

If it were me, I would wait. In fact, there's not always a reason for testing at all if the child is doing well at school, is well adjusted and happy, and accommodations are being made (we tested due to hime being labelled the 'problem kid' etc.) - other than for specific programmes.