Well, I've been one of those teenagers that posted their NSFW art online back in the Tumblr era.
What I can tell is that, first, no kiddo should be posting their real age to a bunch of strangers on social media. Keep that information for yourself and DON'T use your personal accounts or link it to your information be it cellphone or real E-Mail.
That, is something that I would always recommend independently if you make NSFW or not. You're a minor, you're exposing yourself to a bunch of endless strangers on social media, just as you can hide your personal information, they can hide who they trully are, so no personal chats, no need to interact with strangers on such a personal level.
I believe that's the obvious explanation at first, but I know many children don't have "the talk" with their parents regarding Social Media and being connected to the Internet.
Now, about making or consuming R18... Kids begin to be interested in that matters, especially with anime, novels, fanfiction and such so it is not strange nor bad for them to explore it, be it because of curiosity or because they are starting a journey about who they are and what is their sexuality/identity. Something extremely important, besides practicing and improving your anatomy abilities.
The only problem I've seen is the romantizicing of abusive pairings (non con, verbal/physical violence), the hyper sexualization of LGBT pairings at the point of being a fetish even worse than just women or men being objectified.
My only worry would be that kids, especially teenagers get the idea that romance is this, when it's not. Age difference, young-pregnancy, toxic jealousy and possessive partners is something that can be consumed, can be enjoyed in fiction and know that one thing is fantasy and another completely different that in the real world, this is bad, negative and dangerous.
I remember that time where young girls wanted to be "what Usagi-San and Misaki from Junjou Romantica had", young boys wanted to have "yandere girlfriends that would kill for them, be possessive and that held pocket knifes dangerously". And of course those that wanted to be "in love" such as Erika and Kyouka from Wolf Girl & Black Prince.
And that's by mentioning a few well known anime pairings, I didn't even got into the doujinshi or fanfiction field.
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Personally speaking from my experience, teens can make NSFW at least if it were in places where they can avoid comments or personal messages. (I had a Tumblr back then when I created content as a minor, and the only feedback or commentary I've received was from very close friends around my age since my account was private and you needed a password to enter). The only thing I don't encourage is doing NSFW commissions, because that means you'll have to provide a contact info, linked to real information about yourself.
However, as I went through it, I understand that having a mayor emergency can lead to accept to draw whatever comes your way for the sake of having that money but still, I hope that NO ONE has to go through that, especially since most aren't mentally prepared to deal with that, be it the stress of handling money, working with deadlines or drawing stuff quite more extreme than what you're used to.
On my case, I did work while still being a minor but near my coming of age. The only thing that I did was having an open relationship with my parents, talk about this stuff because well, shame is something that doesn't exist on my personal circle (I know, there are lots who doesn´t). My parents only asked me that whenever I feel overwhelmed, to drop it. As well, whenever I accepted a job, they wanted to be when the interactions were made and to help me keep things professional and to don't let the client cross any line.
And gotta mention, I had normal commissions open, but clients of that matter NEVER popped, just people asking for NSFW, which I first rejected but as problems arised, back then I just went "work is work, don't be picky, you don't have the luxury to reject or be selective about the works you accept".
Nowadays I'm an adult, I do NSFW from time to time, mostly if it's artwork for my fellow artists's friends, my oc's or even commissioned work that I felt in the mood to do. I never experienced being targeted for being a woman, or being a young POC adult (23). However, I must mention that everytime I made quite the risquĂŠ, sexy, or even full NSFW content, there is always people just coming to spit hate because they believe I'm a man and that's something I saw in the community lately, depending on the scale of your NSFW work you may be a powerful independent woman that express her sexuality.... or an alienated traitor that only works to satisfy the patriarchy. If you're male, well, you'll receive hate on a daily basis (They'll assume your libido, your sexual experience, they'll shame virginity, sometimes even your mental state, and gosh the hypocresy by doing some non-direct hate against autism, maturational delay and others)
So.... long story short:
Minors who are interested in exploring NSFW Art, that's more than ok, it is fine but it's not something to share with everyone, maybe with close friends or at least have a safe space, non-well known platform to express themselves at some extent (Some artist used to have different nicknames or even art style to don't get caught or identified by some of their followers)
Avoid needing to open these kind of commissions, and if you want or have to, at least talk to your parents or guardian so you know the boundaries, to be safe and still get the expertise. I know, in certain countries it's illegal or fall into a gray area (In my country, there was no especific law against this so I just went ahead and did it)
When I say an emergency to be driven into this kind of work for the sake of having some money, I mean serious stuff: In my case, my mother was about to give birth, our apartment contract was ending and we couldn't find an accessible place, she didn't receive support from my father, family didn't care, no one was supporting us, my sibling's father just puffed and the place she was working on was falling apart and her boss barely managed to pay her salary. I was studying and desperately trying to get a job, but despite applying on every place in my city, I never got called.
It's been 8 years since that, it was hard work and mostly to be tolerant and patient. So while I don't want to encourage or make it sound as a free pass for anyone to do this kind of content regarding of their own personal choices or confort. I gotta say, I'm glad I did NSFW at the age of 15 and I don't regret my choices, I don't regret that any medication, any diaper or anything that my sibling needed we could afford it thanks to it. Doing this allowed me as well to don't feel like a parasyte or depend from a child support that wasn't even the minimum most kids received, that I could do my own stuff, that I didn't need to feel bad each time I had to ask for money even for stuff as simple as using a bus.
Now I live on my own, with my boyfriend. I have a title in makeup, professional haidressing and manicureI. I could go on vacations, make gifts for people I love and I don't hide the fact that I do comics or NSFW stuff, no matter if it's something vanilla or hardcore. Sometimes I even vent about it with my family and it feels nice they don't even flinch at some very graphic details I mention, they only care I'm healthy, I'm independent and doing my own life.
Sorry for the long reply, but it's not only about an opinion but I think it was even a reflection for myself.