Third group is those who don't discuss it, hence they don't lie.
I'm not promoting the taboo topic status, but that's the way in some families. No one wants to hear about that.

I don't care whether people lie or not.

At age five, I discovered masturbating. With four kids, we had a floor checker game with large, semi-soft checkers, about 6" in diameter and 1/2" thick.

I discovered it felt good when I pressed a checker between my legs against my panties. So, I took a checker to bed with me. Pleasured myself until I fell asleep.

"Where's the last checker?" my siblings would ask. "I know!" I said, and ran off to my bed to get it.

You are not truthful on purpose or not... does not matter.

How about those that have dementia and can't remember?

I'd agree it's true for men. Probably about 90% for women.

Yes. I'd give a more detailed response, but typing with one hand is difficult.