As far as your own personal experience is considered, I think you should answer it as just that. Your own personal experience/journey. "Virginity" can be complicated, after all it is a social construct/concept. So, I think you should define that in a way that you're comfortable. Nobody should decide when that was, except for you. Our society likes to form labels, such as "virginity", which are sometimes helpful, but can be just as harmful in some cases. For example, many people also tend to think of "virginity" as penetrative sex between someone with a penis and someone with a vagina, but this isn't true for many queer/LGBTQ+ people. As for your other questions:
1. I think it is up to every individual person to define their "virginity". Many people think of it as the first time they had "sex". This could mean oral, vaginal, anal, or simply making someone orgasm or orgasming with another person. For some people, it may only involve sexual touching with someone else. The traditional meaning of the term is becoming more obsolete. I think that's great! Sexuality is so diverse, not one definition fits everyone. So, I think it is up to the individual to decide what "virginity" means to them, if anything at all.
2. I prefer to say "sexual debut" or "the first time I had sex", personally. I find it to be more positive, but still gets the point across. "Virginity" typically implies something is "lost" or "taken". It enforces the idea that women are meant to be pure in some way. It also sort of reinforces the double standard that men are "cool" for not being virgins, but women are "impure" for doing so. However, if someone uses the term "virginity" in conversation with me, I understand vaguely what they mean and I don't blame them. It is a widely understood term. Still, educating others about the power and connotation behind these words is important. That's why it's great that we have these discussions on a platform like Scarleteen!