Oh I agree if you need it do it! I would only keep in mind the fluctuations and re test later if you don't believe it was an accurate representation of you child. The report can give a good indicator of if it is not representing the kiddo. My DS that had a bad WPPSI had a WJ abilities that show who he was better on paper at that time.

2 of my DC are the youngest in their class by 6 to 18 months. The age has been a nonissue. The lack of challenge and appropriate material has been the real issue.