To me, tickling is not always sexual. My extended family was big into playful tickling, with my parents, aunts/ uncles and older cousins (I'm one of the younger ones) using it as punishments for losing games and the like. When I hit 10 years old I started being able to fight back. I plot with cousins that were around my age to attack all the family members who tormented us wit tickling before especially my one aunt G. Gorgeous lady, very proper, but she tickled the shit out of us. I made a plot to get her and we tickled her so bad she fell off the couch with her feet up in the air face down stuck between the couch and the table. That was the moment I found shrieking laughter so much fun to hear
Next was my cousin cory. She's still my favorite cousin to this day. Now she is 8 years older than me. You can react how you like, but she was absolutely my first crush as a kid. I looked up to her as an older cousin, she had so much going for her athletically and she was so successful already even as a teenager. But she has one of the sexiest figures I've ever seen (I say that as a family member just acknowledging her beauty). As a 10 year old, she was like an 18 year old life guard to me at the pool. I was always star struck around her. We had so much fun together growing up, but she tickled the hell out of me at times. I could never get her bad enough back bc she was so much stronger than me still and I couldn't find a spot to actually make her laugh. She always teased me "there's only one spot and you won't find it." When I turned 14, she was 22, and we were at her birthday party. The family was hanging out later and she was sitting in a chair next to me. I beat her in a hand of poker and tried to poke her ribs, but accidentally poked the space right next to her breast. I was about to apologize, but she damn near fell out of her chair. I jumped on her and vibrated my hands in that spot on both sides, finally claiming to be victorious and that she would never tickle me again or I would retaliate properly.
I frequently used tickling games we made up such as "duck duck tickle" a way to flirt with girls I liked. It was an easy way to feel out if there was mutual desire for physical touch or attraction. I don't think tickling became sexual for me until I had such a physical relationship with a certain girl that just tickling her got me so "excited"
Having said that, I am still able go completely dissociate playful tickling that isn't sexual in any nature with tickling of a sexual nature or tickling with someone that I have a sexual relationship with. I know not everyone is capable of this, and I consider myself quite lucky that I can