What does it mean when some psychologists support the idea that people follow along a continuous path of development?

It is a scientific fact that as people grow older, Our cognitive capability tend to be reduced so our brain is actually started to deteriorate rather than developed

Some psychologist believes that people constantly improve themselves as long as they live even after the cognitive ability started to decline by using their experience (older people tend to have more experience)  to make better decision besides relying on their cognitive capability alone. 

Children typically learn to read during preschool.