Many times.
The first; a babysitter when i was 5 years old.
For the second, see my story, in true atories and in my archives, "First Time Ticklesex".
I have had a total or four long term (multi-year) girlfriends in my 58 years of life. All four have asked me to tickle them numerous times.
A number of the lovely ladies here on TMF have mentioned that they would like me to tickle them. Only one has had that wish fulfilled, and has since repeated the request. I will NOT mention her name. If she wants you all to know, she will tell you.
Gotta be my charm; God knows it ain't my looks or money!