Final answer:
A person is capable of giving consent when they understand the information relevant to the decision and can make an informed choice. Although legally, adulthood typically starts at age 18 in the U.S., sociological and cultural definitions of when someone is considered an adult can vary.
Step-by-step explanation:
When considering when a person is capable of giving consent, the key principle is that it depends on the individual's ability to understand the information relevant to the decision and then make an informed choice. Parents often provide consent on a child's behalf because a child is not legally competent to provide consent for themselves. In legal terms, adulthood, where one can give independent consent for many aspects of life, typically begins at age 18 in the United States. However, this can vary depending on the area of life in question. For example, consenting to medical treatment may have different age requirements than consenting to participate in research.
It's important to note that being considered an adult varies culturally and sociologically. For instance, in some cultures, individuals take on adult responsibilities and are thus considered adults at a much younger age, whereas in Western cultures, the transition to independence and adult roles tends to occur later.