You ask if it's normal to be "so kinky" (a phrase we shall both retire, at least when referring to your son, after today) at such a young age. Probably not—but so what? According to science, most adults have paraphilias, aka "non-normative sexual desires and interests." That means kinks are normal—at least for grown-ups—so even if your son isn't normal now, BANDAGE, he'll be normal someday. Most happy, healthy, well-adjusted adult kinksters can point to things in their childhood that seemed to foreshadow their adult interests in bandages/bondage/balloons/whatever. Author, journalist, and spanking fetishist Jillian Keenan (Sex with Shakespeare) was fascinated by spanking when she was your son's age; Keenan likes to say she was conscious of her kink orientation before she knew anything about her sexual orientation. So while your son's behavior may not be "normal" for a kid who grows up to be vanilla, it would be "normal" for someone who grows up to be kinky.