I dug out my original log, and found 14 flights leading to solo, 9.9 hours, and 32 landings.

1
1
1
1
1
1
2
3
3
3
2
6
3
4

My original instructor was a Delta check airman and former military aviator; primary instructing wasn't his full time job. The training was Part 61, and I was in high school at the time; training was spread over 9 months to get to solo (due to my finances, schedules, etc).

The point is that the nature of the training environment, student, circumstance, frequency of training, your own experience level as an instructor, and your background, all make a difference in the numbers.

My feeling is that a student should be soloed early, as long as the student is safe (and the requirements have been met). The basic requirements must be met, but a student who can be doing solo and training concurrently develops confidence and progresses better than a student who goes extended periods without a payoff. The solo is one of the biggest events in one's flying career, to say nothing of the early student experience, so getting the student to the point where a trip around the pattern can safely be conducted as early in the training as possible is beneficial.