I've been masturbating to my sister's stuff since she was about 14 or so. It started when I realized that instead of reading about girls I could just borrow my sister's used panties and return them later even more used.
As I got older and bolder and went looking for any porn she might have (none that I could find) or a vibrator. Bingo. When we had been kids we used to hind things in the box springs of our beds (small slit in the underside closest to the floor). That's where I found it. I used to borrow it, sniff it and sometime cum on it and then replace it. Between her panties and a vibrator that had actually been up inside her I was in heaven. Once in a while I would leave a bit of cum on the inside of her clean panties or bra(only a bit or I might have been caught) and then think of her wearing them all day.
She has no idea how many times I masturbated to the thought of her masturbating!! I still do!!