I've talked to, and known, a couple of women over age 21 who were not ticklish at all. That being said, when we talk of "ticklish", this is a very broad classification. If this question is meant to ask if girls over age 21 are at all, even a little bit, ticklish, on some spot, my guess would be that number is at somewhere around 95%, as I would venture to guess that very few women are not ticklish at all. However, we then have to break down into the different classifications of "ticklish", from a little ticklish, to moderately, very, extremely, and off the charts. I would say, breaking these down, that probably 85% are moderately ticklish, with at least 65 to 75% being very ticklish, and maybe around 50% of so being extremely on some spot. As for "off the charts", that number is hard to say.
Maybe I'm wrong with my guesses on percentages, but , based on girls I've talked to in my life, these would be my guesses.
Mitch