One recent paper is on the revocation rates of those who are the same age as college students in the states of Michigan, Texas, and Nevada: Concealed Carry Revocation Rates by Age. (The paper mentions other states as well, but according to Lott those states provide revocation information by age).
It is interesting reading, but it contains one statement that surprised me:
The only exception to being age 21 or over to get a CHL that I am aware of is if the 18-20 is a current or honorably discharged member of the military. So far I have been unable to find any other exception.However, in Texas younger people can get special approval if they are facing extenuating circumstances, such as being stalked. In any give [sic] year, there are about 90 to 185 such permits that granted to 18 to 20 year olds.
Is that statement from Lott's paper above correct, or is it a boo-boo? Could it be confused with another state?