This question seems to come up periodically, so I've developed
Redmage's Sexual Tickling Identification Test
It's easy: just answer three questions.
1) Would you be comfortable explaining why you like tickling to a child?
2) Would you be OK with your mother watching you being tickled in the ways you enjoy?
3) Would you talk about your tickling experiences with a co-worker, as you might a sport or hobby?
If the answers to all three of these questions are firmly "YES," then chances are your interest is not sexual.