For years, your GetReligionistas have been saying that the aging of mainline religion — first on the doctrinal left and now in many conservative traditions, as well — is one of the most important stories of our, well, age.

Look at it this way.

Stage I: In the 1970s and ‘80s, America’s liberal mainline Protestant churches went into what now appears to be a demographic death dive (hello Anglicans in Canada). This created a massive hole in the middle of the public square that led to …

Stage II: Evangelical Protestants rise to become the new “it” factor in American life and politics. Evangelicals are still a massive piece of the religion marketplace, but now…

Stage III: Evangelicals are starting to show signs of age and their demographic trends are mixed. Keep your eye on statistics linked to baptisms and converts to the faith. And look at the ages of all those people in the “nones” category.

This leads to this week’s fascinating chart from Ryan Burge of Religion In Public.

Read on.

If you are interested in the future of American religion, then you have to be willing to talk about these kinds of topics — birth rates, conversions and, increasingly, the average age of people in the pews.

In other words, it’s time, once again, to discuss that old saying: “Demographics are destiny.”

GetReligion readers: How often have you seen posts that discuss questions of this kind? The reason we keep bringing this up is that reporters have to be willing to ask questions about issues rooted in demographics — that is, if they want to anticipate future news trends.

That’s true in politics, for sure. You know Republicans are worried about younger voters right now. You also know that savvy Democrats are starting to pay attention to the rising number of Latinos who are worshiping in evangelical and Pentecostal pews.

All of this is, of course, leading up to this week’s thought-provoking graphic offering from political scientist Ryan Burge, who is also an ordained Baptist progressive. Journalists who cover religion need to follow this guy on Twitter and bookmark this website: Religion in Public.

Here’s the Big Idea for this week:

“The average Muslim in America is nearly 22 years younger than the average Mainline Protestant.”

There's no way around it, saith Ryan Burge: Gray hair in the pews is an important story

See that thinning flock of pew sitters with gray hair? That's a big religion-beat trend