I guess my first actual fantasies were about the age of 11 or so. I knew the power of tickling from way before, being extremely ticklish myself, but at that age I began imagining my beautiful female classmates, tied spreadeagled and naked, with me tickling them wherever I want for as long as I want. I could practically visualize their reactions and ticklish suffering.
I didn't know what that meant from a sexual standpoint at that time, but I knew it was getting me very excited.