Teenage happiness carries on well into adult life. Researchers from the University of Cambridge and the Medical Research Council's Unit for Lifelong Health and Ageing used information from 2,776 people taking part in the 1946 British birth-cohort study of people born in that year. When the participants were between 13 and 15 they were assessed by their teachers as to whether they were 'very popular with other children,' 'unusually happy and contented, made 'friends extremely easily,' and were 'extremely energetic and never tired.' The teachers also rated the children's conduct problems - restlessness, daydreaming, disobedience, lying etc - and emotional problems such as anxiety, fearfulness, diffidence, avoidance of attention etc. The researchers then compared these ratings to people's mental health, job satisfaction, relationships and social activities several decades later. They found that teenagers who were rated positively by their teachers were significantly more likely to have higher levels of well-being later in life, including more job satisfaction, more frequent contact with family and friends and more regular engagement in social and leisure activities. Happy children were also 60% less likely to develop mental disorders throughout their lives, although they were actually more likely to get divorced.
You can find out more information about this study here.