Age inappropriate behavior
Age inappropriate behavior are offenses that would not be considered an offense if the person doing them were older, or younger. They are a form of misbehavior that is related to the age of a person — typically a child, adolescent or (mainly in fiction) a young adult.
Too young for it
Children are often forbidden by their parents to do things that they will be allowed to at an older age. This often comes out of concerns for their health and safety. For example, a young child may be forbidden to leave the yard without permission, or to cross the road unsupervised.
There are also laws and regulations designed to ensure that only minors above a certain age threshold, or only adults, have access to certain products, places, and media. Such laws typically criminalize not the action of the minor but that of the responsible person who provided them access to it. Examples are smoking, drinking alcohol, watching video films or playing computer games rated above their age, accessing erotica or pornography. While the minor may not face legal trouble, they can well get in trouble at home when caught, possibly including spanking.
Also many lesser things such as bad manners (e.g. cursing, uncleanliness) can get a child in trouble, while an adult who does the same will not in any kind of legal issues, although society as a whole, especially people one depends on such as family, friends, employers, colleagues and customers, will tend to withdraw support when they feel offended by such behavior.
Finally, there is also precocious behavior; but while such is unexpected for their age, it is not generally considered an offense.
Too old for it
In some cases a child may also be punished for behavior that they are considered too old for. For example, bedwetting is not considered an offense for a young child, but historically, children past a certain age were expected to control their bladder, and failure could result in trouble. Another example is age inappropriate crying. A child might get scolded for crying unnecessarily or excessively (as younger children do), perhaps with the phrase "Stop or I'll give you something to cry about." Such crying might also be seen as faked or manipulative, see crocodile tears.
'Immature behavior' in spanking fiction
A frequent theme used in spanking fiction (from written stories to adult films) involves someone past the setting's normal age for disciplinary spanking, such as a young adult still living at home or staying with an older relative, or a teenager in a setting where teenagers typically receive an alternative punishment. Here they inevitably suffer a humiliating punishment (usually starting in the over the knee position) after exhibiting some type of immature or irresponsible behavior. The typical rationale of the disciplinarian is that anyone who behaves like a naughty child should be punished like one. Often the victim will loudly complain, "But I'm too old for a spanking". This is usually countered with a stern "my house, my rules" reply as the punishment continues to its conclusion.
Underground spanking videos often include the line as a legal disclaimer so there is no ambiguity that the spankee character is an adult. In Visiting Home (from Cutie Spankee in Japan) a divorced girl moves back home and gets punished like a child by her strict mother (see video clip). A similar scenario is played out in Annabelle Back at Home with Mom (Spanking Bare Butts). Sometimes the punishment also includes changing into a juvenile school uniform. For example, in Spanked Bubble Butts (Pacific Force) Gia Regency is forced to wear a schoolgirl uniform for a series of humiliating ageplay punishments.