If you’re getting sexual satisfaction from something above and beyond society’s grasp of sexual stimulant, then, yeah, it’s probobly considered a fetish. But be careful with the word ‘pervert’… it’s harsh and negative (and over-used). Tickling is a form of domination, even torture. If you are a 30-year old uncle who tickles a 5 year old niece without mercy, you’re perverted. If you’re an adult who tickles another consenting adult, more power to you. There are much less innocent fetishes you could be involved with.