My friend's sister.....?

as you can see i have a friend who has really hot sister.i went over ti his house on saturday. no one was at his house exept his sister(whose name is erica) and my friend. erica went out for a jog. and my friend's tutor came. he was gonna be there for 2 hours. so i stayed down stairs watching tv. i got bored so i decided to whip out my penis. while i was stroking my penis, erica came in. i was fast enough to hide em. she was sweaty and wearing one of those tight sports cloths. she went up stairs and i heard a water running which meant she was taking a shower. later she came down stairs and said hi to me. then she told me to tell my friend that she was going out with her friend. when she left i was bored and had about hour and 40 minute until the tutor left. since i was horny and bored, i decided to go to erica's room. when i went into her room she had her sweaty cloths on the ground. so i picked them up and smelled them(i know thats kind of a thing perv would do but i dont know what came over me). her sweat even smelled good. i saw her sweaty thongs too. i smelled them and licked them. i immediately got naked and went on her bed. then i rolled around. i dry humped her pillows. then i went through her drawer and got her thongs and licked them and rubbed them over my body. i went in to her bathroom, and licked the toilet seat and went into her shower too. i also went on her computer too. the i felt like total stalker but i couldnt help my self that this girl is so hot. i started to masturbate while smelling her dirty panties. then i came over her clean thongs. then i got dressed up went doen stairs and took her dirty thongs. now that i think about it, i felt like total pervert. do u think its normal for my age?