Lost it at 19.
I lost a bunch of weight when I was 18 and I was pissed at myself for being a virgin for the first year of college. So I was determined to lose it between the first and second years of college. I was at the music section of Best Buy, where I'm pretty sure I was getting the new Cee Lo album (Cee Lo Green is the Soul Machine) and saw a girl with giant boobs in the same section. I swallowed my pride and approached her. She was very receptive, we talked about music for a few minutes, and got her number. I'm pretty sure I was stumbling all over my words when asking for it but she did. We wound up going on four dates. Before the fourth date, she let it be known that we were probably going to have sex. I never told her I was a virgin but deep down, I suspect she knew (not that it was difficult to figure out lol) so she was helping me out by letting me know (how nice of her). So I remember being embarrassed as hell to buy a pack of condoms so I did the usual "buy a bunch of other shit" routine.
I remember it being pretty uninspiring. I couldn't feel anything at all with the condom and I also jacked off earlier that day since I didn't want to look like a two pump chump. As a result, it was about 30 minutes. I remember having to break once to drink some water. It was not a magical experience. Afterwards I think we just watched TV at her place the rest of the afternoon.
The post script to this is that we went out a few more times but with college coming up, this wasn't a relationship that was going to last. She was 18 and going to some religious private college another state over. The drive time was going to be six hours and I saw pretty much every long term relationship fail so I wasn't dumb enough to assume it was going to work for us. So we broke it off a couple weeks before going back to school. I was still horny so I wound up hooking up with a Latina that I worked with at a throwaway summer job before I went back. After that was a several month long dry spell. That's one of the delusions of the virgin: that once you lose it, you'll keep having sex on a regular basis. Couldn't be further from the truth.