It took Bitcoin 8 years to fill a 1MB block size limit, it would take a few years at least before 8MB blocks start becoming full.
Not nevessarily. Who says the growth will be linear based on the average of all that time?
It took Bitcoin several years to reach 1000$, how long did it took for the next 1000$?
logarithmic growth could make an 8MB block full in the next year, especially since there is already a catch up needed as visible in the high fees.