There are two things that worry me and make me wonder if he’s too young. The first thing is just how uncomfortable he was talking about it. I understand it’s a tough subject to discuss but he wouldn’t even say the word, he had to write out what he wanted to say on a piece of paper. That may go along with him feeling ashamed, which I hope I helped him get over by assuring him there was really nothing to be ashamed of. But I wonder if it could also mean he’s just not ready to take this step.
Additionally, I don’t really think he understands how masturbating works. I don’t think he understands what an orgasm is and I don’t think he is aware of any of the things that happen when one has an orgasm, specifically ejactulation. I’ve considered discussing all this with him and explaining it all, but the idea of talking about sex so in depth with my little brother makes me uncomfortable. I also was thinking that if he doesn’t understand how it works it might mean he shouldn’t be doing it? I don’t want him to do it when he’s not ready and then feel uncomfortable about it after. I don’t want him to feel badly about masturbation because he started when he wasn’t ready.
Like thewrit3r mentioned, masturbation is usually something that starts in infancy (even though most people don't remember doing it), and even possibly in utero. It not only isn't always sexual -- sometimes it's more about self-comforting than stimulating, or just about curiosity about one's body and its responses, especially for children -- but at 12, it's pretty common for people to start having sexual feelings and to express them with masturbation. And how comfortable people feel asking about masturbation or other parts of sexuality isn't a good measure of if they're "ready" to touch their own bodies. More people are uncomfortable -- of every age -- talking about this stuff than not. And I think it's pretty safe to say that unless your home has been really relaxed in talking about bodies and sex, it's not at all unusual for a younger brother to feel pretty uncomfortable asking his older sister about this.
People also don't have to know how human sexual response works to explore it. Most people don't when they first start, and most people learn BY exploring it, later augmenting it with more information, like via various forms of sex education.
Here's the biggest thing: you don't have to worry about him starting when he isn't ready because he already started, probably when he was just a baby, and he would have been ready then, because we all are if that's a thing we're inclined to do (and again, it almost always is). Really, all this is is a person exploring their own bodies with their own bodies: we do that from the second we're born. It's not a trauma, it's just one of the most basic ways of experiencing and exploring life there is, if not literally THE most basic way. Truly.
It's okay.
I agree that this site isn't a great fit if you want to give him some sex ed. We intend what we do for a slightly older readership, so it can just be overwhelming for much younger readers -- it's a lot here, after all -- or those who are super-super new to all this. Instead, I'd suggest giving him some resources meant for younger readers. Books-wise, my friend Cory Silverberg's book "Sex is a Funny Word" may be a good fit, especially if in your family no one really has been candidly talking about body parts and sexuality pretty openly all along. I can also suggest some puberty books if no one has yet given him anything like that: it's certainly time, if not.
Online, there's a newer video series that I think is really quire perfect for his age group. You can both check those out here:
https://www.youtube.com/channel/UCXQZTt ... H2fg-OJ_eA
There's even one on masturbation specifically:
https://www.youtube.com/channel/UCXQZTt ... H2fg-OJ_eA