I was 18, or maybe 17 (it was about 1976). I caved to peer pressure, and was just glad to get it over with. Looking back, I would have been far better off being introduced to sex by an older, more experienced woman. Like most late teen males I could cum 3-times in an hour, and was about the same size physically then, as I was at 30 (6'2", 185#), so plenty "adult" enough in that respect.
She was about my age, or a bit older, and the Minister's niece, visiting from out-of-town. :-o (I grew up in a very liberal church environment.) She said she was a virgin too, but I later realized she was probably just saying that to make me feel better (nice touch, and it worked). One of the condoms tore (she was very tight, and I was overly enthusiastic), but we got lucky. (Mother Nature's design is spectacular!)
We did it several times over several days (late nights actually) on the couch in her Uncle's house, while her grandfather was upstairs. :-)) The uncle (the minister) was out-of-town. Fun times. :"> She encouraged me to go down on her orally and I declined. (I was completely clueless & uneducated.)
The peer pressure was from some guys in my Boy Scout troop (there may have even been an adult leader present). The conversation went something like, "Boy, you must be pretty lame if you cannot get laid by the time you are 18." The statement was not directed at me, but I put a lot of pressure on myself to meet that goal. I have been a late bloomer in many respects. I would have been better off waiting.
Water under the bridge however. It is what it is.
My first meaningful sexual experience was with a woman my age, when I was about 22 (after I got out of the military). She had a lot more experience than me, and the 3 years we spent together was good. She really liked to be pleased orally, and trained me well. :-p I have never looked back since.
:-D