Islam has the largest number of under-30 believers in China?

Christian Today has a post up with this headline.
The lead statement says:

Islam has the largest number of young believers in China, new research has found, despite the growth of Christianity in the country and an atheist government.
The China Religion Survey 2015, released by the National Survey Research Centre at Renmin University of China,  found that 22.4 per cent of Muslims in China are under 30, with Catholicism following closely behind at 22 per cent aged 30 or under.

(My emphasis added.)
The article is getting some linkages and was referred to me by a friend involved in ministry there. It appears to me the lead is unclear, and in its unclarity, wrong.
I think they said “largest number” when they meant something more like “largest percentage” or “largest share.”
Let’s do the math:
Muslims in China number at most 24.4 million.
If 22% are under the age of 30, then under-30 Muslims number about 5.3 million.
Catholics probably make up about 20 million (both Asia Harvest numbers and the World Christian Database agree on that).  The study cited seems to suggest Catholics also have about 22% (slightly under Muslims) of their membership under 30. So Catholics would likewise have slightly fewer people in absolute numbers: 22% of 20 million = 5 million.
But Protestants number 84 million.
If even 10% (half) were under 30, then under-30s would equate to 8.4 million.
If 20% are, under-30s would be 16 million, or 3x the number of Muslim under-30s.
It’s not likely that less than 5% or so of Protestants are under the age of 30!
This article in Breitbart goes further:

The study, conducted between 2013 and 2015, found that 22.4 percent of people under 30 years old identified as Muslim, while 22 percent identified as Catholic. Buddhism and Taoism were the two most popular religions among people over 60 years of age.

Now, precisely how many people does “22.4% of people under 30” equate to? The UN has China’s population by 5-year age group, as of 2015: 0-4, 91.2 million; 5-9, 85.2 million; 10-14, 78 million; 15-19, 82.6 million; 20-24, 107.8 million; 25-29, 133.2 million. Add these together: 578 million. 22.4% of them are Muslim? About 130 million. That’s about 6 times the total number of Muslims in China right now, or about 10% of China’s population. If they were all under 30… that would be a massive people movement, and how would that be ignored and suddenly discovered in a research study today?
Anyway, the Breitbart report cites this Global Times report, which says “Islam has the largest number of young believers, with 22.4 percent of them aged below 30.” So Breitbart gets it wrong through unclear writing.
However, I think the Global Times report is wrong too, since it claims most religious Chinese are younger. There are 1.4 billion people in China, and if 578 million are under 30, that leaves about 900 million who are over. A good chunk of those would be Buddhists and Taoists, and you have to count them as religious. Without doing extended analysis, my money’s on there being more older religious Chinese than younger – invaliding the Global Times statement.
What I think the original study was saying is this: of all religious groups, Muslims in China have the highest percentage of members (not the highest absolute number of members) who are under the age of 30. Or, more simply stated: the average age of Islam is younger than any other group. I haven’t seen the original study yet, so I don’t know for sure, but this is about the only thing that isn’t immediately falsifiable. Muslims do tend to have a higher birth rate, which would skew toward a younger population.
Another possibility: Muslims in China may very well be the fastest growing religion among Young Chinese, too. Small groups do tend to be faster growing than large groups, so this would be unsurprising. Rapid growth when small is not maintained when groups become large, however.
This just goes to show that we need to be careful in how we say these kinds of things, and just think for a moment about what’s being said.