You're underestimating the age of the fleet.
The average GA aircraft is 50 years old, and that is likely to increase in the near-medium term as production of GA aircraft is practically zero.
Source: https://www.ainonline.com/aviation-news/business-aviation/20....
(Cirrus, mentioned above, produces about 300 aircraft a year - compare to the 100,000+ Ceessnas on GA fields, almost all of which are over 40 years old.