That's a good question.
Maybe you picked something you were comfortable doing.
I'm not a cutter, either. Not for lack of trying- I just can't make myself do it. I either hit myself, or burn, and usually burn lightly, at that (but not always, it depends on the reason). It's not the type or degree of self harm, sometimes, it's that you're willing to purposely damage yourself in some way.
The burning, I began doing after having hit myself for sometime, the opportunity was there, it was convenient, and I just decided to do it- then it became a habit.
Like you I'm an apparent late starter- I say apparent, because while I didn't seem to start hitting myself in earnest, until late 40s, thinking back, I can see where I was on the verge of being a self-harmer, at least a few times, back when I was late teens/early 20s, but it wasn't the addiction that it has become.