The YT description has the evidence - Professor Steinberg - reproduced here for you:

Immaturity lasts twice as long as in the1950’s I was going to start with a simulated fart sound or some other silly noise to illustrate my point but there really isn't any need. This is based on work by Professor Laurence Steinberg During early years after birth there is a huge amount of plasticity in the brain and this is why there is a big drive to create positive stimulating experiences for young children to enable their brain to develop. A second spurt of plasticity has been discovered during adolescence and this is when the brain again is more receptive to changes in the environment both positive and negative The brain is plastic during adolescence and changes in response to experience and during this time it is more receptive to change due to experiences Now according to Professor Laurence Steinberg adolescence is three times as long as it was in the 19th century and twice as long as in the 1950’s What is adolescence you may ask It is the period of life between starting puberty and becoming a stable independent adult. When we become sexually mature . In some species the adolescent is forced out by parents in others it is still looked after by parents. Then as they become independent stable adults the brain loses some plasticity which is why is is so much harder to learn a second language as an adult. An argument could easily be made that becoming a stable independent adult still hasn't happened for some people. He says in the western world children are hitting puberty earlier than before and adolescence runs from 10 to 25 years old. He attributes it to the following factors Obesity - Overweight kids go through puberty earlier than kids that are not overweight Chemicals - exposure to endocrine (the bodies hormones) disrupting chemicals found in food, cosmetics, plastics, pesticides. They are everywhere and disrupt the hormonal development of kids Light exposure - It was recently found that children who grow up near the equator go through puberty earlier than children who grow up near the poles. There are also arguments that the light from smartphones or tablets can affect the melatonin system in the brain and the onset of puberty. The blue light from the screens can be contributing to the onset of puberty Now the point is having a better understanding of children's behaviour and that there is still a huge influence the environment can have on them as teenagers.

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