What is an adult?

Is it someone who has passed a certain age, or is it someone who has demonstrated respect for others, responsibility in dealing with others, and self-sufficiency in the lack of external authority.

We label an 18 year old an adult, yet we withhold the privilege to drink alcohol until the age of 21. Why? Because the federal government refused to give the individual states money for the improvement of highways unless states raised the legal drinking age to 21 years of age. This was done because politicians thought that fewer intoxicated teenaged drivers would make our highways safer. How does our government justify declaring that a child becomes an adult on his or her 18th birthday, and then try 16 and 17 year olds that are accused of serious crimes, as adults? The government seems to realize that the arbitrary mark is unrealistic and uses a marker of whether that child is able to understand the consequences of his or her actions. I would argue that a person who knows the consequences of his or her actions are detrimental to others yet acts regardless, is either still a child, or something akin to evil. That person has demonstrated neither responsibility, nor respect.

Self-sufficiency can be demonstrated as individuals, or through a spousal relationship. If a couple working together are self-sufficient, then both individuals are as well. A person can forge their own way through the world, or can have the wherewithal to find someone to take care of them. If someone married a person who lived with his or her parents until the wedding, never having to supply for himself or herself, would that person still be a child, or would the marriage make them an adult? After the marriage the couple must still be considered for self-sufficiency, but the individuals still bear the other two criteria for adulthood.