Agree with everyone it depends on the person. I’d always been self conscious about my belly button, so in addition to being sensitive to the touch, the psychological aspect of being “embarrassed” has always made my belly button and surrounding area more ticklish. I know it’s coming and can’t help it.
That said, I know some that want nothing to do with their belly button being touched for reasons mentioned above, but their belly is ticklish.
Then you get those that aren’t ticklish on their belly button, but a raspberry there or blowing air as already mentioned drives them up the wall. I think it half tickles and half laughing at the absurdity of it, but that’s just my experience.
Pinpointing ticklish spots and reasons behind them is impossible to categorize