Inability of an individual or a group to perform the given tasks up to the established standards. http://www.businessdictionary.com/definition/deficiency-performance.html.
TSA Requirements. The TSA requires that adult passengers ages 18 and older show valid photo ID at the security checkpoint. Children, however, are not required to present such identification. This does not mean, however, that children will be able to fly without it.
The age limits and ID requirements vary by carrier. Delta and American Airlines, for example, only allows children 15 and older to travel alone domestically without their unaccompanied minor service (See References).