Anything between 1 hour and 50 hours! There have been numerous threads on this in the past, mostly ending up being a competition with more and more ppruners giving fewer and fewer hours before their solo.
If I said the average was 5 hours, what does that tell you? That you're "better" or "worse"? What if the average was 10? 20? Or 3?
It all depends on the attitude of the instructor, the frequency with which someone flies, the nature of the aerodrome and its own requirements (i.e. between learning at an international airport or small airfield), the student's age and how quickly they have picked up things as well as their ability and confidence.
Cheers
Whirls