I've got this from a book named "Foot: a playful biography" by Kathy Vanderlinden
"The great Egyptian female pharaoh Hatsheptut (who reigned 1503-1482 BCE) is said to have prepared for lovers by having the palace eunuchs massage her feet with scented oils, then tickle the soles with peacock feathers."
Of course this might just be a myth made up in more recent times... the truth will probably never be known, yet, this must be the oldest mentioning of (feather)tickling.