Seems odd that a feeling of wellbeing keeps going up after age 40 until age 70. Maybe it's relief from kids leaving the house. There has been recent research supporting the notion of the depressing nature of childrearing.
http://medicalxpress.com/news/2015-11-mi...y-40s.html
http://medicalxpress.com/news/2015-11-mi...y-40s.html