Oh, I think there is no doubt cuckolding/ hotwiving really hits its stride in the couples 40/50's. Like you say, most have got a lot of the baggage of their relationship/ life out of the way, and are then will to expand their desires. I think most try swinging in their 20's or 30's... but cuckolding has a much more power imbalance than swinging, because the hubby gets to fuck nobody apart from his hand, so you have to get past all the jealousy/ frustration/ honesty issues before cuckolding can really work... and I think that usually happens in your 40/ 50's.
In my 20's my ex-wife HATED my small cock, and it was the reason for so many arguements/ sadness/ frustrations for 17 years. She basically hated having sex with me, and rarely did, so not a great way to live in a relationship. 25 years on, my current wife LOVES my tiny cock... not because it satisfies her (it doesn't and we are lucky to fuck 4-6 times a year even with a condom on) but she loves to power/ control/ humiliation/ submission it has on our marriage and that her pussy is treated like the crown jewels when I do get to touch or taste it... plus that i'm locked into a life of permanent monogamy to her is the cherry on to for her