Not sure about others but they probably accept under 18s.
Our school Huayang Academy accepts children, we also have close connection with the top provincial University and sent over 150 students there on scholarship this year alone.
(please note that not all of these students studied with us)
From asking students you should check Decathlon or TaoBao. Taobao has clones of tents, bags etc. which are very high quality at low prices. But of course there is rubbish too
Welcome to drop into our school in the next semester, after August 26th. We have many cyclists, climbers, mountain climbers etc. Few have trekked in the high mountains to the north. Drop in lunch time ( 12.30-1.30 ) and have a coffee I'm sure you'll find someone.
We have many cyclists in our school Huayang Academy welcome to drop in or possibly Barfly on Xuefu road there are often cyclists there they could put you in touch