Well, you're 20, and they're as young as 12. To my mind, there is nothing wrong with you talking to them.
But there are a lot of ignorant people out there online who as I say, will look at you being 20, them being 12-14, and get the totally wrong idea, and get the wrong end of the stick. This is an unfortunate circumstance, because of all the bad guys and jerks online, and we get tarred with the same brush as them.
Case in point, when I was finishing high school and was 16/17, I became good friends with some people who'd just come into high school and were like 12/13. That came about because of me being behind in social development more than anything else. But even with that age difference, people got hysterical about it and got nasty ideas about me.
Also I was a regular on a chat site, admittedly I was a bit older than you at the time, at 28, though you say some of the guys on the forums you frequent are up to 30. I have to say, I had a very happy time indeed on that site. Most of the people there were young teens, and I became great friends with quite a few of them. I did nothing untoward, yet I ended up having no choice than to leave, because the following things happened in a short space of time:
1) One of the ops on the site got suspicious of me, and was dropping quite clear hints about it.
2) The fathers of two of my friends from the site came on to talk to me, to confront me, have harsh words with me, warn me etc.
3) A friend (closer to my age) of one of the people on the site came on to give me abuse and threaten me, for talking to this person.
So I speak from experience.