I was lying naked on the bed with Jill straddling my erect cock. I looked at her 57 year old body, her naturally hairless cunt, her hips which had thickened slightly, her waist which still carried no fat, her breasts which though larger were still firm as they all were when I took her virginity 40 years ago. She smiled wickedly down at me and gently pushed her moist opening onto my cock. The feeling sent shivers down my spine. Slowly she lowered herself onto my full length. She was firm, warm and moist. Her muscles gripped me tightly as she leaned forward and gave me a long lingering kiss. Carefully she lifted herself until my cock had almost left her and then sharply dropped down once more. She repeated this several times, getting the feel of my cock inside her. With a sharp in take of breath she began rock back and forth increasing her speed as her first orgasm broke. She released her usual strangled groan as she shuddered on my cock. This was my join in. I pushed and pulled with her. Getting faster and faster. I soon felt my climax nearing and I pulled her down on to me hard and has her hips hit mine I shot string after string of sperm into her. She collapsed on top of me, body twitching and breathing as heavily as mine. What a great fuck my sister-in-law is.