This is in fact false.
It is a misconception that adults experience emotional turmoil during their 40's and go through a so called 'mid- life' crisis. Adults in their 40's are actually a lot more emotionally stable than in their 20's or 30's as many are now in situations in life that are ideal for them. Many are not but more so than less are. Also people are living longer and 40 is no longer considered to be mid-life and there are still many opportunities open for people at this age. People in their 40's also tend to be more comfortable in their own skin and with who they are and they are a lot more confident.
