The Hui number nearly 10 million, half of the country's Muslim population, according to 2012 government statistics.
In Linxia, they have historically been well integrated with the ethnic Han majority, able to openly express their devotion and centre their lives around their faith.
Women in headscarves dish out boiled lamb in mirror-panelled halal eateries while streams of white-hatted men meander into mosques for afternoon prayers, passing shops hawking rugs, incense and "eight treasure tea," a local speciality including dates and dried chrysanthemum buds.
But in January, local officials signed a decree — obtained by AFP — pledging to ensure that no individual or organisation would "support, permit, organise or guide minors towards entering mosques for Koranic study or religious activities", or push them towards religious beliefs.
Imams there were all asked to comply in writing, and just one refused, earning fury from officials and embarrassment from colleagues, who have since shunned him.
"I cannot act contrary to my beliefs. Islam requires education from cradle to grave. As soon as children are able to speak we should begin to teach them our truths," he explained to AFP.
"It feels like we are slowly moving back towards the repression of the Cultural Revolution," a nationwide purge from 1966 until 1976 when local mosques were dismantled or turned into donkey sheds, he said.
Other imams complained authorities were issuing fewer certificates required to practise or teach and now only to graduates of state-sanctioned institutions.
"For now, there are enough of us, but I fear for the future. Even if there are still students, there won't be anyone of quality to teach them," said one imam.
Local authorities failed to answer repeated calls from AFP seeking comment but Linxia's youth ban comes as China rolls out its newly revised Religious Affairs Regulations.
The rules have intensified punishments for unsanctioned religious activities across all faiths and regions.
Beijing is targeting minors "as a way to ensure that faith traditions die out while also maintaining the government's control over ideological affairs," charged William Nee, China researcher at Amnesty International.
Another imam said the tense situation in Xinjiang was at the root of changes in Linxia.
The government believes that "religious piety fosters fanaticism, which spawns extremism, which leads to terrorist acts — so they want to secularise us," he explained.
But many Hui are quick to distinguish themselves from Uighurs.
"They believe in Islam too, but they're violent and bloodthirsty. We're nothing like that," said Muslim hairdresser Ma Jiancai, 40, drawing on common stereotypes.
Sitting under the elegant eaves of a Sufi shrine complex, a young scholar from Xinjiang explained that his family had sent him alone aged five to Linxia to study the Koran with a freedom not possible in his hometown.
"Things are very different here," he said with knitted brows. "I hope to stay."