Srila Prabhupada speaks on the objective of varnasrama
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]. "
Lecture on Srimad-Bhagavatam 6.1.12, Honolulu, May 13, 1976
Srila Prabhupada : "From five to ten years, gurukula. And after ten years, they should go to the Varnasrama College. "
Morning Walk - Vrindavana, March 14, 1974
Srila Prabhupada : "So after brahmacari, one can marry. But that is not obligatory. He may remain naisthika-brahmacari for whole life"
Talk with Bob Cohen - February 27-29, 1972, Mayapura
Srila Prabhupada : "They're not meant for outside work. "
Room Conversation with Sanskrit Professor - August 13, 1973, Paris - See more at: http://bigvc.org/GurukulaAdmission.aspx#sthash.OCyb2Tah.dpuf
Comments by Prabhupādanuga devotees of BIG & BIVC
"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. "
For more details, please refer to Q.No.11 in the Magazine - Back to Srila Prabhupada's Gurukula