Initially the child is given temporary admission for 6 months. If the child gets well adjusted, then permanent admission is given.
" Therefore in the Vedic civilization the children, they are taught from the very beginning brahmacarya. Tapasa brahmacarya.A small boy, five-years-old boy... That is gurukula. Brahmacare gurukule vasan danto guror hitam [SB 7.12.1]. "
Srila Prabhupada : "From five to ten years, gurukula. And after ten years, they should go to the Varnasrama College. "
Srila Prabhupada : "So after brahmacari, one can marry. But that is not obligatory. He may remain naisthika-brahmacari for whole life"
Srila Prabhupada : "They're not meant for outside work. "
- See more at: http://bigvc.org/GurukulaAdmission.aspx#sthash.OCyb2Tah.dpuf
"As we can see from the above quotes the training of children should start from the age of 5 and in some special cases it can even start from the age of 3 or 4 also!!! "
"Boys and girls (from the age of 5 to 10 years) are studying together but they live separately. The girls normally live with their parents who are living in the grihastha ashrama area which is next to the BIG campus or in some special cases the girls are living under the care of elderly matajis. There is no separate hostel for girls. "