They were amazed at the constancy, but it is not inevitable. The fact that it is the half way point may be a factor, and the fact that many dreams of youth are no longer possible eg too old to repay a home loan. No doubt there are those who have had more realistic dreams.
Experience can shatter many illusions. There is the bright side in that after a point people can realize they are too old to dream, and start living each day as though it is a bonus.
What worries me is after being classified as depression, there can be a determination to classify it as an 'illness' or a 'syndrome' that can be remedied with medication, to the point where people become depressed without the medications (which can often be addictive)
Often the only thing that is needed is time. After realizing you're 'over the hill' it is a matter of accepting the inevitable, and making the most of the ride.