My non expert opinion would be that: 1. the test is for that age range, otherwise it would have had an upper limit of 7 years 2 months, or something else. So, it should have been valid.
Also, from everything I've read kids don't accidentally score really well on these tests. Kids do often score inaccurately low for a lot of reasons.

https://twitter.com/asimom, https://contributingfactor.wordpress.com