The short answer is yes, there are instances or circumstances when it is appropriate to treat a juvenile who has committed one or more crimes as an adult. The definition of a minor is loosely based on somewhat arbitrary determinations of when a human being can reason at the level of a mature person. In the United States, a minor is determined to be somebody under the age of 18. There has been a movement over the past decade, however, to revise upwards the age at which an individual can legally consume alcohol from 18 to21. Similarly, the age at which American citizens can vote in elections was lowered from 21 to 18 with adoption of the 26th Amendment to the U.S. Constitution in 1971. Finally, the age of consent for sexual relations is considered in some states as 16, and in others as 18. Defining a “minor,” then, for the purpose of criminal procedures is equally open to interpretation.
Whether to treat a minor as an adult in a criminal case is contingent upon the nature of the crime, the age of the juvenile, and psychological determinations of whether the juvenile understood the consequences of his or her actions. With the age of 18 being the line between juvenile and adult, it is entirely arbitrary to deny that a 17-year old who commits murder, rape, robbery, or any other serious crime should be tried as a juvenile on the sole basis of age. By the same token, attempts by prosecutors to try a 14-year old for a serious crime may involve far more complex and emotional considerations.
There is no “one size fits all” answer to the question of whether and when to try a juvenile as an adult. It must, and is, handled on a case-by-case basis. Some crimes, though, from some minors warrant treatment as though the suspect is over 18 -- even if he is not.