hmm..well It is often confusing to determine if something is a primary source. Materials that are of course not primary sources...include: Books written after a historical event by someone who was not involved in the event. Books are considered Secondary Sources.
Dana (30) most likely due to people becoming more stable in "Mid-Life," A range from around 25-45. It starts to become unstable around 50, so my guess would be Dana (30)
