It’s been my experience that, when a woman sucks on her own thumb, it’s a kind of silent signal to the man that she’s looking to suck on something else, before the evening is over.
I remember dating a gal who was like that. She had sparked my interest in her, when she had said, “I need to let you know, right up front, that I don’t swallow on the first date.”
The oldest thumb sucker I've known was 77 when she died, and wouldn't you know it, with her thumb in her mouth. It took EMS some time pulling it out since rigor mortis had set in. As for it being unusual to be an adult thumb sucker, it's not. A website: www.thumbsuckingadults.com proves that handidly, or should I say thumbidly....
Oh, I should know (by the way) since I’m 58 and still suck my thumb. It’s quite a comfortable posture and provides an instant calm that only a thumb sucker would know, unless you draw analogies to other habits considered more adult like overeating, smoking and others.
I say thumb sucking is far better, not to mention cheaper, legal, convenient and what not.