My stepdaughter is in her final year of studying medicine. I was always a supportive dad, but I didn’t know what to think when I found myself being the subject of some of her medical tests. Apparently, she needs to do a paper in sex studies about longevity. Since my second wife talked to her about my sex game, my stepdaughter thought about asking me for help. She told me the only thing I needed to do was to sit in her room and not cum. Well, then she started taking off her clothes. I always thought my stepdaughter looked hot, but seeing her massive cans for the first time felt amazing. She wanted to see what kind of stimuli I needed to jizz. She grabbed my hand, placed it on her big succulent tits, and made me rub her young nipples. Not going to lie, it felt great. But since I was nowhere close to cumming, she felt she needed to step up her tests. She took her pants off in front of me. Her shaved pussy was staring me right in the face. Fingering her pussy felt really good, but again, it wasn’t doing it for me. The next thing was to test me with a handjob as I was getting out of the shower. As she noticed my cock getting even bigger she even placed her lips on it and started sucking. My stepdaughter has excellent blowjob skills, but it took ticking my cock in her tight pussy for me to finally cum. My stepdaughter got fully naked and climbed me. My cock slid into her wet slit and she began moving, grinding her clit, milking my cock with her vagina. The view of her magnificent tits bouncing around on top of me was amazing. Her weight with every down stroke drove her pussy hard down onto my cock so that it felt that I was penetrating her to the full. She got on all fours and told me to fuck her doggy style. I slammed my hips against her ass, watching as her black ass cheeks bounced from my thrusts. As I was getting closer, the naked girl kept screaming she wanted me to cum inside her. Once I did, I started to suspect this had nothing to do with science. Instead, she just had a huge crush on me.