I know a few schools (and taught at one) where there is a pre-requisite minimum of 25hrs before solo, and a good thing in my opinion. Yes, some people could probably safely solo before this time, but everyone including the student felt all the more comfortable from covering sloping ground, EOL's, PFL's, emergencies in the circuit including downwind auto's from 500' & on the climb out, sideways and backwards flight. As well as this additional handling time, someone who is new to aviation takes at least this much time to truly interpret any situational awareness of others in the circuit and on the radio. They have not had a student solo accident to my knowledge, ever. If someone was particularly keen to try and solo in less, then personally I'd be wary of their attitude. Staying alive is key, and moving a few exercises to pre-solo doesn't cost them any more, they just have less to complete later in the course
