Speaking on behalf of a well regarded and popular instructor on the
West Coast, he once commented to me:
"I've noticed that the average number of flights to solo is about the
same as the age (years) of the student. And once you get past age 50,
some students can never be soloed."

Now I assume he meant those students who are not transition power
pilots, nor ones who had a few flights when they were much younger.
YMMV.


Kemp