Your experiences have particularly caught my eye, because the change of your wives' ticklishness may really explicate a phenomenon.
Specifically, from my perspective, the change of your wives' ticklishness (throughout time/age) is genuine, because such a change has it cause(s).
And the primary cause, in my opinion, is the change of your wives' attitude to getting tickled:
In the early time, your wives had relatively most positive attitude to beting tickled by you, partly because their strong interests and/or appreciations in you. This accordingly brought up their positive emotion/mood to you holistically, which including your tickle fetish. The positive emotion/mood thus genuinely enhanced their ticklish reaction (especially when they're tickled by you).
However, through age, your wives' general interests in you have somewhat dimmed, which may especially embody in their less positive attitude to getting tickled by you. It has made them have a bit more unacceptable or even repulsive emotion/mood when they're tickled by you in some situations at least, which leads them to have obviously less ticklish reaction.
In other words, I think that many lees's emotions/moods can have significant affection on their ticklish reactions. Such an affection is genuine. The change of your wives' ticklish reactions is genuinely caused by the change of their emotions/moods.
You may read this relevant thread of mine:
Though I don't have much experience of real tickling, I've concretely perceived that ticklishness is more variable than constant for most people.
A typical source of my perception is my observation on my peers in school & university.
Specifically, I observed most of those peers getting tickled mostly on their waists in my childhood & teenagerhood. Most of them did have obvious ticklish reactions in some (perhaps most of) time, but on the other hand, reacted obviously less ticklish or even virtually non-ticklish in some other time.
The second source concerns the 'self report' that I saw...