We waited with DD (until she was 8) and tested earlier with DS (having learned from our experience with DD). He was tested at age 6.
Both are now DYS.
It sounds like your DS has already had some testing that confirms that he is at least gifted and perhaps HG+. Would more testing give you further information?
When DD was tested at age 8, we found out she met YS criteria - but that alone did not help us deal with her tendency to challenge authority. That's just a fun bonus we get with her.
Seriously, though - the testing helped us understand that she is extremely intelligent, but her personality is completely different than her equally intelligent (but more people-pleasing) brother. Testing changed none of that, and honestly did not help us to conquer the problem. Only patience, consistency, and lots of deep breaths have helped there...
