Now as an adult, if you break the law, you will be tried as an adult and can be sentenced to an adult prison. Additionally, your parents are not required to support you (unless a court orders otherwise). Furthermore, because you can make binding agreements with others (called contracts), you can also now be sued. United States citizens at least 18 years of age may be called to jury duty. Finally, all males must register for the selective service within 30 days of their 18th birthday.