AITA For Having Been Online Friends with a 14 Year Old?

The title sounds really bad ik, but this is basically what happened: I just turned 18, but I’ve had this online friend (calling him M just for simplicity) for a few months. When I first started talking to him, I was 17 and had just accidentally talked to another 14 year old, so I asked M how old he was and he didn’t want to tell me just because he didn’t know me that well yet. I thought this was a little weird, but he said he was in high school and as I mentioned, we didn’t really know each other that well yet. I did let him know that I was almost 18 and told him to just stop talking to me if we had a big age gap, but he didn’t. I think I forgot how stupid young teenagers are at times, and I should’ve been especially aware of that because I was talking to an 18 year old at 14 too. I’m 90% sure I told M about this and how creepy it was for that person to be fine with talking to me at 14, so this feels all even more insane.

We became pretty good friends after that, and since our mutual friends were 16-17, I assumed M must have been that age too. He mentioned missing being in 10th grade, so I realized he must have been in 11th grade and was thus 15-16 (he moved around a lot, so idk what the grade-age conversions would exactly be). When M was dming my sibling, who was 14, he said he felt weird because they were so young, so once again, I thought he was 16. His birthday was early in the year, so that would mean he was turning 17 soon, and it wasn’t that bad for me to be friends with someone a year younger than me in my opinion. My reference point was that I had friends irl who were 2 years younger than me, so 1.5ish was fine. We weren’t talking about anything really sexual, but we would make a lot of jokes about mpreg and slightly explicit things (saying we wanted to crack a celebrity, sending slightly suggestive fanart/fanfiction, but nothing that was never about each other of course).

Nonetheless, I was suspicious of the fact that he never outright told me how old he was. I would bait him a little bit over the months by sending him goofy ahh birthday cakes I knew he would find funny that would say 17 or 16 on them and see if he would say anything about turning those ages soon. He didn’t! Against my will by now I had also seen his feet and thighs. I mentioned being uncomfortable with that, but I think he just thought it was a joke. I was scared, though, since I still didn’t know his age, so I had enough and asked him if he was 15 or 16. I don’t want to be friends with someone younger than 16, but if he would only be 15 for a couple more months, I would MAYBE be able to. Turns out he’s 14! He also dodged around the question a lot, so I think maybe he knew I wouldn’t want to be keep being friends with him if he was that young.

I also asked some of our mutual friends if they knew how young he was, and they thought he was the same age or older than us too. Idk what to do at this point, because I feel really bad and don’t want to talk to him anymore, but this was also a really good friend of mine. I’m leaning towards not talking to him much anymore, but idk. I’m not sure if I should’ve seen this coming and was the asshole for assuming he was 16ish for so long.