Incest confession

[suryadh]

Once evening i come from Gym, my parent was out of home and only me and my younger sister present at home. I decided to take advantage of it. I took bath and went to my room only on towel for wearing cloths, that day i didn't lock my room's door and keep half open. I turned on tubelight and remove towel. Now i was full nude. I took oil and massage my penis. Now it was fully erect. Now i was waiting when my sister go to kitchen from hall to see through half open door. Just in next to 3, 4 min she went into kitchen in front from my room and due to half open door and light was on, see saw me fully nude in position with fully erect cock  and after 5 to 10 sec see went back to hall staring at my room and she again got full view of my nude body.

What happened next ? How old is she ?