Dr. rich is a psychologist who studies social influences on behavior. she has published 10 articles and 3 books in the past three years, which is quite an accomplishment for a psychological scientist. this is probably because her is currently at its peak.

I believe the answer is: fluid intelligence

fluid intelligence refers to the form of intelligence that allow us to utilize our logic to solve the problem or identify the patterns that we never encountered before.
For most people, fluid intelligence would peak when we enter middle age and would start to deteriorate from that point.