Я пока не вижу причин для такой уверенности. Вот единственное релевантное ограничение, которое я нашёл в законах Висконсина:

Restrictions on hunting and use of firearms by persons under 16 years of age.

Статья 29.304(3)b
Restrictions on possession or control of a firearm. No person 14 years of age or older but under 16 years of age may have in his or her possession or control any firearm unless he or she:
1. Is accompanied by his or her parent or guardian or by a person at least 18 years of age who is designated by the parent or guardian;
2. Is enrolled in the course of instruction under the hunter education program and is carrying the firearm in a case and unloaded to or from that class or is handling or operating the firearm during that class under the supervision of an instructor; or
3. Is issued a certificate of accomplishment that states that he or she successfully completed the course of instruction under the hunter education program or has a similar certificate, license, or other evidence satisfactory to the department indicating that he or she has successfully completed in another state, country, or province a hunter education course recognized by the department.

16 лет, Карл! Клёво у них там, в Висконсине! И с какой стати они будут применять законы Иллинойса на своей территории?

Не понял. На чьей территории человек находится, те законы на него и распространяются. Чтобы иметь экстратерриториальность, нужно быть дипломатом.