Lowest I ever saw was about 10hrs, highest about 100hrs to solo.
The thing a lot of people forget is that its not a contest, from a safety point of view you are ready, when you are ready. Higher hours to solo don't always mean low ability, sometime perhaps they do, but so what if you are that bad hopefully your instructor or school will tell you (from UK experience i doubt they will).
I'll see if I can find the stats I did a year or so ago to support this, from a school I worked at once.
V.