How do I explain to others that it's not their concern if I choose not to have sex?

As someone who waited until marriage to have sex, this was a particular nuisance in my life, as well. I had to explain to people that it was my choice and that I have a right to that choice, regardless of whether it fits within people's expectations of me based on social conditioning. It is important to advocate for yourself and to set boundaries when people are trying to convince you to change your lifestyle due to their own desires or to mollify the insecurities they may hold from making different life decisions from yours. Definitely emphasize that it is your right to do so, and refrain from speaking or acting in a judgmental way of others for not taking the same path as you. We are all part of the human family, and in order to reach out to that kernel of humanity we all share, it is important to focus most on what we have in common rather than that which divides us.

It's your body and you decide what to do with it. It's the same with getting a piercing or tattoos. If they have a concern that you're harming your body then that's a different situation, but if you're not doing anything that could negatively affect you then just tell them that what you're doing or not doing is not causing you harm so it's not their place to tell you what or what not to do. Tell them that if they suspect that you're harming your health then you'll give them the time of day but other than that they should just mind their own business. Simply as that x

As an asexual... I feel this. It's incredibly difficult to constantly be asked invasive questions any time I mention my sexuality, rather than moving on from the topic. But the thing is, nobody can decide your own sexuality for you. Because it is your body, and there should be absolutely nobody else who chooses what you should do with it. Likewise; it's your consent. And nobody should take that away from you. We live in a society very much obsessed with sex so the outliers get a lot of negative talk from people who not only don't understand it, but also choose not to understand it and rather would discuss if it's a real thing to not want to have sex.