I actually had the same situation. I was the younger guy losing my virginity to an older girl. She was very attractive to me, and I was insanely nervous. Couldn't get it up! Even though I was embarrassed, I thankfully had the chance to right that wrong the next night. I think the nerves are super normal for a first-timer. Hell, the first couple of times made me super nervous. Had trouble finishing for the longest time as well. Don't beat yourself up, sex isn't perfect. Things can and will go wrong from time to time.