Adolescence is the period of transition between childhood and adulthood, and it includes physical and psychological growth and development, and gaining experience in preparation for adult status. While puberty, the biological changes in a young person's body, is indisputable and occurs in all people, the concept of adolescence is much more culturally based. Most would say that adolescence ends when adulthood begins, but there is no universally accepted measure of when exactly that happens.
There are legal markers of adult status, such as the age at which one may vote, join the army, marry, drive or buy alcohol, or the age of criminal responsibility. Many groups have ceremonies marking the entry of a young person into adulthood, but the age at which this happens varies greatly from culture to culture. In some cases, it overlaps with the beginning of physical maturity, at around age 12 or 13 (such as in the Jewish or Moslem communities). In others it is nearer the end of puberty, anywhere from 16 to 21 years of age (think 21st birthday celebrations). In yet others, adulthood is attained through trials and tests, and therefore may happen at different ages for different people.
Generally, in Western society, we consider age 18 to be the end of adolescence. It approximately overlaps with the end of puberty and the start of legal majority. However, a study published in 2003 shows that Americans today define adulthood by the following factors: financial independence, leaving home, finishing one's education, and working full-time [source: Furstenberg et al].
Many people today do not reach these milestones until they are well into their twenties, leading to the question: Are they still adolescents up to this stage, or have we perhaps started identifying another transitional stage of "young adulthood" in which one is no longer adolescent but not yet fully adult?