I don’t have scholarship to point to, but it seems intuitive to me that the devout will find it harder to give up their religious beliefs as they age. The older you get the more invested you are in your beliefs, and this for at least two reasons:

First, you have literally invested more time and energy in it. Every time you go to Church, every time you say prayers at night, every time you make some personal sacrifice to live out your faith, you are that much more invested.

Second, insofar as your religion promises some comfort in the face of death (like the promise of an afterlife) the nearer you get to death, the more you will rely on those religious beliefs for comfort.

The more invested you are in something the harder it is not just to let it go but even to envision letting it go.

Additionally, I suspect religious beliefs become habits. They give us fixed points we are used to falling back on amidst uncertainty, like a banister in a house we’ve lived in for decades that we instinctively grab for in the dark; the difference is if you make a mistake with the banister (and grab for it after it gets taken down), you are promptly corrected by reality, but you don’t get that immediate correction when you grab for an unverifiable belief that isn’t fact.

I doubt there is a magical, externally observable threshold past which a person cannot change his religious beliefs (just because human psychology is too complicated), but I suspect that the longer you have believed your religion, the more you have given to the practice of your religion, and the more you come to rely on that religion for comfort, the more difficult will it be to countenance the possibility that it is false, until at some point you find it simply unthinkable.

this is not my own personal experience.

Well, I suppose it wasn’t true in my experience either.

I suppose for myself I’d chalk that up to two things:

First, I don’t get the same emotional investment in things simply from putting time into them. I know this is little bit weird about me. I have worked on computer programs for months and then realized I hadn’t thoroughly planned it out and that what I had been doing was consequently fatally flawed, and then simply walked away from thousands of lines of code with a shrug. Once I realized the problem, there was no period of denial or desperately trying to find a way to salvage it, but simply a resigned, “well, it is what it is”.

Second, my engagement with religion was not principally devotional. I mean, I sincerely believed it, and I did practice it, but no one would identify me as having an especially profound piety. My engagement was principally intellectual, academic, and driven by curiosity.

A final consideration is that I’m not sure that, had certain incidentals been different, I would have felt the freedom to inquire as hard as I did. I mean, a whole host of factors had begun to dissolve my deep sense of tribal alliance with fellow Catholics; I want to be clear, this isn’t the reason I decided it was not true, but it may have been a but-for condition of my eventual apostasy. Had I felt the social bonds as strongly as I had earlier in life, I might not have followed the inquiry where I did.

Does any of that sound like something that might overlap with you or your father?