I cant confirm this, because it was a pen pal I've never met, but several years ago before I joined TMF, I knew this one pen pal who told me that she wasnt ticklish at all, anywhere. She said that when she was younger, she used to be deathly ticklish on her feet, but by the time she became like 20, she just lost it. I have a feeling she may have been telling me the truth, because of all the letter pen pals I've had and asked the question to since 1996, she and one other girl were the only people who claimed they werent ticklish, while 99.9% of the others said they were.
One other thing: This can be confirmed. My ex girlfriend who wasnt ticklish, told me that when she was a teenager and younger, she also used to be ticklish. (This was confirmed by both her brother and her parents when we all used to try and tickle her while she and I were going out, and she had little or no reaction) Her family claimed that up until her mid to late teens, she used to be like "notmal" ticklish. If not very or extremely, then at least enough where she would laugh if someone tickle attacked her bare feet. Then, suddenly, about two years before I met her, when she was like 17, she just lost her ticklishness. She never had any accident or nerological issues, it just happened. No one, not even my ex gf, had any clue why.
I do think based on what I've seen and heard that ticklishness can be gained and lost. Some people are always ticklish, while others may be at some time and not at others. I think it really depends on the person. In the two cases I mentioned, especially with my ex gf, those are cases of girls who used to be ticklish, and then lost it and became non ticklish for some reason.
Mitch