Welcome!
Your best source of information is likely the normative information provided by CTY, especially since it is their intellectual property, so not much is available outside of them. I did find one research article that cited some of their 1999 normative data, which indicates that the mean score obtained for 3rd graders (on the elementary level of the test--which would have been administered to typical grades 3-5 for in-level testing, and by CTY to 2nd and 3rd graders for out-of-level testing) was 23.6 and 20.9 for verbal and quantitative, respectively. For 5th graders (which are the group CTY uses as a comparison), those mean scores were 31.5 and 29.7.
As the standard deviations were not listed, it is not possible to derive the percentiles that you are seeking. (For 3rd grade.) According to the CTY website, the percentiles you received should be the 5th grade percentiles.
Based on what you have reported, it appears your DC is quite good at quantitative thinking, as that is approaching the ceiling of the elementary level. And obviously not too shabby at verbal thinking either!
General caveat on grade-level norms here: these were published in 1999, so they are at least 20 years old, and thus likely to be subject to norm obsolescence for the use for which they were originally developed. CTY's internal data on their use for identifying students likely to be successful in their programming for advanced learners is much more current, and thus likely to be more useful.
