I'm also on the older side myself. To be honest, I didn't really have this fantasy myself growing up. I only really discovered it after I started reading hentai manga. I came across the NTR genre (which is basically cuckolding) and then started finding stories that dealt with mothers cucking their sons. What's funny is that I feel like the genre itself has sorta "grown" with the internet as there was a time when stories like that never existed, and then slowly but surely more and more stories began focusing on it. Kinda like society as a whole started to acknowledge the fetish at the same time lol.
I find it incredibly exciting that these days the internet has essentially given any age group the chance to discover this site and educate themselves on this fetish. Meaning there could very well be high school boys on here, learning about this fetish, while still living at home with their moms, fantasizing about the school jock, their friends or even their actual bully fucking their mom and jerking off to it. Getting off to porn, comics and stories about their moms getting fucked by their classmates, their bullies, their teachers, while actually still living their daily life in that environment. Learning and allowing themselves to embrace this fetish in their formative years of puberty, and yes, maybe even making an attempt at fulfilling this wonderful fantasy at one point before they have moved out of their parent's/mom's place and it's too late.
I'll go one further and suggest that what's even more hot to think about isn't boys developing this fetish. But MOMS starting to develop this fetish. I think this might be tied to the earlier point about how society seems to be discovering this fetish, I think a large part of that has to do with how women and their sexuality post motherhood is being redefined now. There was a time, 30+ years ago, when a woman became a mother, for all intents and purposes, she stopped being a sexual being in the eyes of society. Their sexuality was never talked about, always downplayed, almost nonexistant. We live in a world now where that's not the case. Where just become women become mothers, that doesn't mean they stop getting horny.
I know there's no reason to believe me, hell, I don't even believe fully believe it myself sometimes, but I've actually met (online) an actual mother who had this very fetish. What's funny is that she had no experience herself with NTR hentai, which I think is how most of us came across this fetish. She just naturally always had this fantasy, it was kinda a love/hate thing where she would fantasize about doing super dark, messed up things to her son, in front of him, but at the same time holding him in her arms, saying she's a good mommy while cucking him.
I'm not saying that's a common thing going around or anything, it's still very niche, and even more so for women and actual mothers. But I do think it's something that's slowly becoming more common.