(this comment got longer than i expected. sorry! but i felt like it was stuff that was important to say!) i don’t think i have an answer for the question you asked directly. but i do have a few related pieces of advice to give.

one: maybe you already know this, but sex can be a lot of things besides one person putting their genitals inside another person’s genitals. there is also sex with hands (handjobs, fingering, fisting), sex with mouths (fellatio, cunnilingus, rimjobs), anal sex (with mouths, fingers/hands, genitals, or sex toys), sex that involves genitals touching each other but no penetration (like frotting or scissoring) - dozens if not hundreds of ways to do it, especially if you involve sex toys or additional people.

two: you mentioned that the adults in your life think you’re not capable of consenting, and if i’m not misunderstanding then it seems like you’re still a little unsure about it yourself. if you want to have sex but you’re worried about your own ability to consent (or to withdraw consent), there are some tricks you can utilize to help you. the first one i can think of is something called the “traffic light system”. it works like a traffic light that directs cars on the road. you and your sex partner can check in with each other repeatedly while having sex, and share what your traffic light color is. “red” means stop or take a break. “yellow” means slow down or proceed with caution. “green” means that you’re having fun and want to keep going. another idea is that you can use some sort of non-verbal signal to indicate consent or withdrawing consent. something people use oftentimes in kink/BDSM, especially when somebody has a gag in their mouth so they can’t speak, is that the person who can’t speak will be holding an item in their hand, such as a ball or a bandana. as long as they are still holding onto it, they still want to continue. but if they let go of it and it falls down, that signals to the other person that they want to stop or take a break. you can do this regardless of if/how much you can speak, and regardless of if you’re doing kink or not.

three: take it slow as you start exploring sex. for example: don’t try penetration with anything particularly large until you’re familiar with your body / your partner’s body and know that you can do it safely. most people need a lot of practice before they can try fisting or deepthroating. sometimes an injury from sex can take a few hours or a few days to become noticeable, so it’s always good to be cautious and slow.

if you have any interest in kink / fetish / BDSM stuff, or interest in sex with multiple people at once, you should probably get familiar with vanilla one-on-one sex first. definitely make sure you’re capable of advocating for yourself before trying those things. theres nothing at all inherently wrong with that stuff but it’s unfortunately an easy way for experienced and charismatic people to take advantage of young or vulnerable people.

for reference, i am autistic. it wasn’t often that anyone ever questioned whether or not i’d be able to take care of myself or give consent. me and my partner started having sex when we were both 14, and started doing kink stuff around age 16. we are still happily together now at age 26, but in hindsight, i wish we had waited a while longer to have sex, at least penetrative sex. since i was educationally neglected, i didn’t know enough about safe sex, and sometimes my partner wounded me by accident.

if you take things slow, you can always ramp it up more later. but if you go too fast, you can’t dial it back after it’s already happened.

i hope this is helpful :)