This post is going to prove to you the following hypotheses:
1) The physical world is retarded
2) The homo sapien is the most retarded animal
3) The homo sapien displays behavioral neoteny
1)
This one is quite easy for the student of electromagnetism. The physical world (at least our conception of it) being structured largely with the concepts of extension and duration, aka distance and time, is thus by definition structured with electromagnetism and light. The implications of this are widely referred to as "special relativity". The wave equations describing the propagation of electromagnetic disturbances aka light admit two families of solutions, which go by the names "retarded" and "advanced". To put it simply, all the light we observe (be it by the nature of our observing platform or otherwise), is of the former camp. Light diverges from sources and not the other way around. So yeah, the world is retarded. Information takes a while to reach you and is less clear for taking the time to do so. Your image of the world is delayed and you will never catch up. Lame huh? Them's the breaks, get used to it.
2)
This one is quite easy for the current parent (please note: no elided "genetic" is implied here). In this case the hypothesis posits a relative retardation. There is no a priori reason why an animal learning the standard method of locomotion in one revolution of the Earth about the Sun should be considered slow, but it is amazingly slow in comparison to most of our brethren in kingdom animalia. The current parent has probably been advised by well-meaning passers that "They grow up so fast". Well, no, pointedly we do not grow up fast - at least in comparison to any other animals. What the well-meaning passers are saying politely is that we are all going to die and life is but a passing instant, enjoy the moments for they all pass. Correct them next time.
It is worth noting and somewhat ironic that it is the retardation of our neural development which in part enables us such amazing feats of mental gymnastics. If we had to produce all wetware programs that we run in the first few days post conception, our abilities would be rather limited. This is kinda one of those tortoise and hare issues ya see. Because we are slow to develop, we have more time to learn. And we wind up better for it in many ways.
A passing galactic hitchhiker from Andromeda for example might be offered two creatures to take home as a pet. A one month old chimpanzee and a one month old homo sapien. One might forgive the hitchhiker for choosing the chimp based solely on intelligence. Developmentally, the chimp is quicker. In fact all animals are. With reference to our first hypothesis Einstein famously quipped that most people understand things like distance and time very quickly in pre-school, and that he was much slower. The result is clear: he kept at it and wound up with a better understanding than most. Humans are developmentally retarded, and it allows incredible brilliance to emerge, provided the development continues. Sometimes the word "retarded" is used to indicate not just a slow-down but a full stop (or asymptotic or harmonic stop). In that case, well, you wind up with a developmentally locked individual. There are important places in society for such, and places that such should stay away from, but I digress.
3)
This one is kinda a subset of the previous. "Displaying adolescent characteristics as an adult" seems a phrase specifically crafted to describe human behavior. Actually the word was not created for the homos, as far as I can tell. It really is more of a clear cut term amongst animals that have more of a metamorphosis thing going on, in particular so there is physically a difference between the adult and the adolescent. In the humans, there isn't much physical neoteny in that adolescents look structurally identical to adults. However, behavior is where the real interest lies.
There are advantages and disadvantages to behavioral neoteny as well as different interpretations of my claim. An obvious advantage is allowing learning to go on longer, and drastic changes to be made later in life.
The term has a sexual connotation because as homo sapiens much of the distinction of adulthood and adolescence revolves around these behaviors. Adolescents, due to lack of experience, often have misconceptions. Anyone who is ever upset, angry, or thusly emotional in any way solely due to any persons engaging in voluntary sexual behavior of any kind, is an adolescent. That's a strong claim, read it again. Note that if somebody lied to you about their sexual behavior, and then you found out the truth, the emotional response is not "solely due to sexual behavior". It is due to being lied to or whatever else. "OMG my wife fucked some guy! I'm gonna go be a violent dumbass!" Who cares? Grow up. Healthy grown primates have sex every day, adult ones are never upset by it. Interested, yes. Curious, yes. Jealous, yes. But angry? Upset? Adolescent behavior pure and simple. A good use for the word "neoteny". "Oh but we had an agreement where she swore she would pick me up at the hospital and she didn't show because she was banging the garedener!" Well that is something different. It doesn't matter if she was banging the gardener or watching a soap opera, in terms of whether you got picked up at the hospital or not. This is a good place to observe neoteny, as you can see clearly this sort of behavior exhibited by all sorts of prominent would-be "adults".
You know, I had no intention of getting into that argument at the start of this. Perhaps my behavior is showing a tendency to be attracted to sexual topics. Is that adolescent beahavior? BTW I've heard tell some adults still drink milk, is that neoteny or what? Cross-species neoteny even: exhibiting behavioral characteristics of immature bovines.
It may be that human behavior at one time had a clearly delineated adult stage, and was therefore not neotenous. Most societies in which wisdom and literature were not under attack (by book-burners who never bettered the first enemy of knowledge, aka colonialists) maintained a strong ritual of adulthood, usually involving facing danger and in some way understanding the fundamental hostility of the world, amongst other important things. From what I know the modern Bar Mitzvah or Sweet 16 ceremonies do not involve large doses of psychedelics, nor starvation, nor long periods of isolation, nor difficult physical feats. So we are left with a population more neotenous than ever. Them's the breaks.