How many fundamental rights in the Bill of Rights can be uniquely regulated for adults under 21?

The answer to the question in the title of this post would seem to be "at least one" in light of an interesting ruling today by the Seventh Circuit in Horsley v. Trame, No. No. 14-2846 (7th Cir. Dec. 15, 2015) (available here). Here is the starting, ending and some in-between key passages from the panel decision:

Tempest Horsley’s application to possess an Illinois Firearm Owner’s Identification Card, commonly known as a “FOID card,” was returned to her as incomplete because she was over 18 but not yet 21 and her application did not contain a parent or guardian signature. Although she could have under Illinois law, she did not seek further review from the Director of the Illinois State Police. We disagree with Horsley that the Illinois statutory scheme violates her rights under the Second Amendment. Illinois does not impose a categorical ban on firearm possession for 18-to- 20-year-olds whose parents do not consent. Rather, when an applicant cannot obtain a parent or guardian signature, he or she may appeal to the Director for a FOID card, and the Director will make a determination. We conclude that this process for 18-to-20-year-olds is not unconstitutional, so we affirm the decision of the district court....

Horsley ... maintains that firearm possession by 18-to-20-year-olds falls within the scope of the Second Amendment. She emphasizes that persons over 18 can vote and serve in the military, get married without parental consent, and own land. Even though the age of majority was for many years 21, it is now 18, and so she argues that presentday 18-year-olds cannot be restricted from possessing firearms based on age alone. She points to historical evidence that she contends favors her position as well. The First Militia Act enacted by the United States Congress in 1792, for example, included 18-year-old men in the scope of those eligible for the militia. Because a minor could be a member of the militia and be armed, she reasons that the Second Amendment gives these persons a right to bear arms. We need not decide today whether 18-, 19-, and 20-year-olds are within the scope of the Second Amendment. Cf. Nat’l Rifle Ass’n, 700 F.3d 185 at 204-05 (also declining to resolve issue). Even if they are, our next step would be to turn to means-ends scrutiny of the regulation. Ezell, 651 F.3d at 703.... Significantly, although Horsley’s arguments treat the challenged statute as a categorical ban on firearm possession, the FOID Card Act does not in fact ban persons under 21 from having firearms without parent or guardian consent. Having a parent or guardian signature may speed up the process, but it is not a prerequisite to obtaining a FOID card in Illinois. Rather, a person for whom a parent’s signature is not available can appeal to the Director of the Illinois State Police [and any] denial is subject to judicial review....

The absence of a blanket ban makes the Illinois FOID Card Act much different from the blanket ban on firearm possession present in Heller. That there is not a categorical ban here also distinguishes this case from Planned Parenthood v. Danforth, 428 U.S. 52 (1976), to which Horsley points. There the Supreme Court struck down a “blanket provision” requiring the consent of a parent or person in loco parentis before an unmarried minor could have an abortion during her first 12 weeks of pregnancy unless necessary to preserve the mother’s life. Id. at 74....

The Illinois statute is substantially related to the achievement of the state’s interests. The goal of protecting public safety is supported by studies and data regarding persons under 21 and violent and gun crimes....  Trame also points to scholarly research on development through early adulthood that supports a conclusion that the Illinois FOID card application procedure for persons under 21 fits the state’s compelling interest in public safety....

We conclude that Illinois has shown a sufficient meansend relationship between the challenged statute and an important government interest.  Illinois’s decision to use parents as a first check on firearm possession by persons under 21 is reasonable.  The parent or guardian signature provision provides for an individualized assessment of the applicant’s fitness for possession of a firearm by a person likely to be in the best position to make such an evaluation. That signature also subjects the parent to liability for harm caused by firearm ownership.  The legislature could reasonably conclude that many persons under 21 would not have the financial ability to compensate a person injured in a firearms incident, and the signature provision in the Illinois statute provides a means for an additional source of income in that event.  If no parent or guardian is willing or able to sign the application, the Illinois statute provides that another person can make the individualized assessment — the Director of State Police.  The challenged provisions in the FOID Card Act are substantially related to the state’s important interests, and we do not find the law unconstitutional.