Around this same age...maybe 12? 13?...I was also sneaking into my mom's clothes a lot. She was working a lot so I had the house to myself, and I would sneak into her bathroom and try on underwear. 

I didn't get much of a thrill wearing her bras but I liked to smell them after she wore them, they were powdery smelling. I could imagine her tit scent. 

I found it very quickly that putting on her panties and especially her pantyhose was tricky because it got me too excited. Like I could not figure out if she wore panties under or over panty hose, so I put pantyhose on first over my naked and throbbing dick. And the feeling got me so hot that I had to yank them down to cum. I remember the cum dripped on my leg and felt so good running down the nylon.