I was about 11 years old.
I used to tie up my friends with my jump ropes. A few times I was questioned by my parents when they saw my jump ropes coiled around a kitchen chair I had taken into the family room to tie up a friend. Boys, girls, it didn't matter to me as long as I could tie someone up.
When I became a teenager and wanted more rope, I went to the hardware store and got a 100 foot package of "sash cord" and cut it to lengths I liked. At first my rope bondage was sloppy, but effective. As I got more experienced, I figured out how to make it more elegant. When I was in college, I got a couple of books on it and got really good at it. I really like rope harnesses that typically use 50 to 75 feet of rope. I liked being tied up too.
For the last twenty years, I have been getting my rope at West Marine. It's more expensive than hardware store rope, but it is MUCH better quality, handles better, and is available in many different colors degrees of softness, flexibility and braid patterns. I also like to tease the salesmen who try to be helpful by asking what I am going to use it for on the boat. Usually I tell them it's to tie up my husband, which is the truth, but they generally laugh it off until they say, really, what are you going to do with it and I assure them it's to restrain my husband.
I always use waxed cord to whip the rope ends and then seal it with liquid whipping or heat it with a low temperature (yellow flame) "blazer torch" to prevent any fraying of the ends. It also makes the ends oh, so pretty! We have at least 500 feet of rope in the house in different lengths, colors and diameters.