I was 14 when I lost mine. I remember it so vividly to this day..(some 36 years later...lol).

I'm not sure if I regret the actual act of the sexual experience itself, but moreso, the act of carelessness on my part...wasn't on the pill, which my very first encounter ended up in pregnancy.
What I do harbor mostly from it was the fact that my mother refused me to keep the pregnancy, (a direct contradiction to her Cathoic behavior for self).
She scared the hell out of me by telling me that if I were to follow through with having the baby, that I'd be kicked out and left alone to raise. That she "paid her dues by already raising 10 of her own and wasnt about to raise another". At 14 that alone was enough to influence me into having an abortion, (a procedure that had soon afterward been banned and illegal), and something which will forever remain embedded into memory.

Regret isn't exactly something I carry for any given situation I've encountered. I try to seek out the required lessons and learn from them.

Although, I do encourage for anyone to always evaluate your reasons for the choices you are considering, as the consequences of your actions are something you must contend with.
Good choices = favorable consequences.

Shangrala