More unformed thoughts on those rough times (3 1/2-year-olds)

So I've been thinking a lot about this 3 1/2-year-old thing. And how it really seems to me like all the "difficult" stages seem to be at times that double: 4 months, 9 months, 18 months, 3 1/2 years, 7 years, 14 years. I don't know if that means anything, except that if you're 28 maybe you're having a tough time, too. And 56 might also be rough...

Anyway, it seems like the difficulties start out more weighted toward the physical but become progressively more emotional as the people get older. So that first rough stage at 4 months is mostly about being fussy and not being able to sleep. Then at 9 months it's not sleeping but more generalized crankiness. 1 months seems to be a tie between physical and emotional distress, and then by 3 1/2 it really seems to be mostly emotional (even if all of this is caused by some physical process of development in the brain).

It feels to me, from being on the outside of it, that the developmental spurt that's happening somehow seems to remove the protective emotional layers somehow, so that all the person's emotions are right there, waiting to bubble over at any second. The person on the inside can't process or deal with or control them. Which is why they get stuck in a "Pick me up!! Put me down!!" loop. It's like they have an exposed nerve, and any time anything brushes against it they just go off from the overload.

I've noticed that when I'm feeling emotionally fried, my child being in one of these emotional wack-out times just sets me off, too. But when I'm on an even keel, my response just instinctively seems to be more one of "Oh you poor sweet little thing. Let me give you a hug."

Does this resonate with anyone? About any of the stages? About yourself? Or do you think there's something different or more going on?