The average hiker averages 20 miles a day over the course of a 152 day thru-hike, including zero days.
Fewer miles in the beginning is the norm. Bigger miles per day as your trip progresses. 15-20 is very normal in the beginning.
Check out the planner. It will help you plan a hike according to your style:
https://www.postholer.com/planner/Pacific-Crest-Trail/1