Be young to be admitted

[faa2010]

These issue has been argumented and discussed a lot and since the beginning of ages.

I don't want to mean that all the music schools have the same though, but the majority like the conservatoires and the ones of "high" prestige demand that the only students who can enter to study music should be of a younger age (in my country, our conservatoire's condition is that the ones who enter should be between 12 and 15 years old).  However, as I perceived, others also want to enter, but due to either economical or personal problems, they cannot enter until a mature age.

Of course, there are other conditions that can make the admission "unreachable", but this one is very curious.  Why do some schools put as part of the admission to be younger?