...start masturbating at a very young age?

I started probably around 3 or 4 years old. I have heard that some children start at a young age due to sexual abuse, but I was never abused. I am curious as to why I began so young, while my siblings had no interest in it.

Masturbation is the only way I experience sexual pleasure, as I am an asexual and have no interest in sexual activities with others, whatsoever. I'm totally fine with that, and since I have many years of self-pleasuring experience, I consider myself quite the expert.