I met my Daddy/boyfriend online in a very platonic way. Perhaps you will end up in the same place I did.
I played a game online and felt kind of lonely so I asked other players to chat with me as we gamed. My Daddy answered my request and we had some small chit chat.
We became friends and eventually grew closer over a few months. Throughout our friendship we had both lighthearted and serious discussion. Right before we became "officially" a couple we had a discussion about interests and weird things about ourselves. I knew I could trust him but I was still cautious at that point.
I threw out that I had a silly thing for calling boyfriends "Daddy" playfully at times. He responded with a, "Why?" and I said, "Ah, it kind of ties into this ageplay thing." He didn't know that term and I passed it off as, "Just, like, when you're kind of roleplaying as an age you're not really."
So, I tried to brush it off in the end of the conversation as, "Ah, I'm just kind of silly sometimes and act kind of younger than I am is all." It peaked his interest though and he had noted it as something I was interested in.
He was a pretty vanilla guy though. When we started dating I playfully teased about some kink things and he wasn't very much interested in anything non-vanilla.
Then, one day, he threw it at me that he had search around for this "ageplay" thing and learned more about it. He said he was interested and wanted to tie it into our relationship. I then brought him to more specific terms and ideas. He was really interested and encouraged me to connect with others in the dynamic too.
And that was that.
So, the answer is--be careful. Be friends first. Close friends. Even closer friends. Get to know the person. Take your time! Share personal things back and forth as you two grow in a platonic way. Toss out tidbits and test the waters first before you come out and say it. Also, be prepared to answer questions!:
http://www.littlespaceonline.com/app.php/page/comingout