https://en.wikipedia.org/wiki/Armed_Services_Vocational_Apti...
The first time I took the test as a dumb 17 year old who was at risk of failing out of high school my GT score was only 107 (out of 130) and my average performance placement compared to all other test participants that year was 79 (on a scale of 0 - 99). Generally, everybody who entered the military as a teenager notices dramatic improvement on that test when retaking it later life even with no preparation.
When I wanted to become a warrant officer I had to retake the test because of my low scores. The minimum GT score to become a warrant officer is 110. I retook the test at the age of 35 after 8 years of being a full time software developer in the corporate world. My new GT score was 129 (out of 130) and my placement amongst other test takers that year (on a scale of 0 - 99) was 98.
I think research generally bears this out across a variety of metrics and meaures including violent crime data. The human brain is still developing until around age 24 give or take two years. This is why applaud California's recent decision to halt standardized tests, such as SAT and ACT, as a mandatory placement criteria for entering university. All those tests measure, given the youth and maturity of traditional high school students, is extreme preparation and not performance or potential. Preparation in that regard is a socio-economic stratifier as it takes time and money outside of the student's own initiative and state provided education.