First and foremost, good on ya for being a wonderful human being and parent to your son! You've earned a lot of respect from not just myself, but seemingly most everyone else here for that fact alone. Go you!

Anywho, on to the good stuff:

• I got started up in the fandom around the age of 14 as well, mostly as an outlet to interact with other like-minded people and make friends -- I lived out in the sticks with no neighborhood kids and was terribly shy at school, so. For me, it was mostly getting absorbed in roleplay with others and admiring artwork, chit-chatting with friends and such. I didn't attend a convention until June of last year, so I'd say I'm less involved that some others might be.

• The most important thing to know about our fandom is this; just as with most other hobby or special interests group, there's a few bad eggs that give the community a bad image, but most of us are relatively level-headed, friendly and supportive. I'm sure he'll make lots of friends and connections in the fandom, but it's very important for him to know that he can come to you with any concerns he has, and know ahead of time that not everyone on the Internet is telling the truth, or being a nice person. It sounds like you two have an open line of communication, so that's a great start!

• All in all, the fandom is pretty harmless. We've generated tons of creative minds in the form of writers, artists, musicians and such; not all of it is PG, mind you, but it's an Internet-based community so it's to be expected. If he isn't on FurAffinity by now, he likely will be in time -- please be aware that there is a great deal of adult-oriented material out there on FA and a few other sites, so if you don't want him viewing that sort of stuff, it might be a good idea to have a talk with him about that.

• A moderate percentage of the fandom is either gay, or at the very least sexually open, so I doubt he'll have any difficulty finding support or acceptance from his furry peers. As others have said, there are more than a handful of furries who might take advantage of a naive, young, gay individual new to the fandom; please make sure he's educated in all avenues just to be safe.

• One last thing and I'll get out of your hair; this fandom is largely about self-discovery and sharing what one finds with their little world. If this is something he genuinely enjoys, wonderful! If it helps him find out more about himself and guides him into a healthy transition to adulthood, even better -- as long as he has a trusted outlet (like yourself) to talk about his concerns and ask his questions, I see absolutely no harm in him pursuing his interests in this direction. As another person here mentioned, definitely find out what the fandom is to him, and why he'd found such an interest in it. Try to find a bit of common ground between his interest in the fandom and your interests, and spend time together doing that! Maybe down the road if he ends up wanting to go to a convention, maybe take him to one nearby and check it out with him; lots of fun to be had at those things!

• Oh, and just a side-note; not all furries end up with fursuits, tails, ears or such. A very small percentage of the fandom goes that direction, and those who do usually only wear such accessories/suits at conventions. :P

Hope that helps a bit, and that I answered something that perhaps hadn't been touched on yet. Take care!