Wow, this is fascinating. I wonder if the results are linked to this study:
The students were also shown photographs alongside descriptions of various crimes and asked to assess the age and innocence of white, black or Latino boys ages 10 to 17. The students overestimated the age of blacks by an average of 4.5 years and found them more culpable than whites or Latinos, particularly when the boys were matched with serious crimes, the study found.
This study was brought up in the article discussed in this thread about the disproportionate discipline of young black children, which you might be interested in. I have a strong intuition the results of these studies are intrinsically linked.