My mother was always under the belief that tickling is a form of torture. She never let my brother or I be tickled by other family members (or each other) if she could help it.

en.wikipedia.org

Tickle torture is the use of tickling to abuse, dominate, humiliate or even “prank” someone. The victim laughs even if he or she finds the experience unpleasant because the laughter is an innate reflex rather than social conditioning.

It doesn’t really mention it in the article otherwise to say “the fun stops” at a certain age, but I never thought it was much fun to begin with.