Mainstream religious affiliation is on the rise, and has been for a number of years (PRRI, GSS) and the median age of a white evangelical Protestant is higher than any other denomination.
I did not know that, and it surprises me frankly.
The study had a flawed methodology. It considered all people who self-identify as Christian but not as Evangelical or Catholic to be mainline. So what is almost certainly actually happening is younger non-denominational Christians who don't like labels are getting lumped into their "Mainline" category. There has not been any kind of corresponding increase in membership in mainline denominations.
Poll
