Liking Transformers is a good start. Beyond that, it's all up to personal taste. Whether one prefers Beast Wars to Generation One, whether one buys zero toys or all the toys, whether one identifies with the Autobots or the Decepticons, whether one makes twenty posts a day to Transformers boards and newsgroups or has never visited a single forum... that's all irrelevant. The term "true fan" gets thrown around a lot by people who seemingly can't understand that there are people out there with different preferences that aren't in any way "wrong". You know the type: "Beast Machines is a bad show, so, anybody who thinks it's better than Beast Wars is just messed in the head." Or, for a more classic example: "No true Transformers fan would put up with that Beast crap."
The only quality in a fan which is widely agreed upon as important is open-mindedness and willingness to give a chance to Transformers material that they haven't seen without dismissing it as stupid. Transfan Matt "Thylacine 2000" Greenbaum said it well in a post to alt.toys.transformers: "As far as I'm concerned, being a fan has nothing to do with how dedicated you are or how much you know; instead, it's a question of attitudes. If someone legitimately thinks that ONLY the stuff which he/she happens to know about (read: remembers from childhood) really counts, and that everything else sux.... well, they don't belong here."
After a rather influential message by M Sipher in 1997 the term "true fan" has taken on a whole new meaning among some TransFans. It's a sort of twist on Godwin's Law where anybody who accuses somebody of not being a true fan automatically loses any argument, and is often discounted as a buffoon afterwards. The point is, there is no correct way to be a Transformers fan. There's not even "better" ways. A fan is a fan is a fan. Deal with it, Magnus.
Sure. The two main options are "TransFan Code" and the "Transformers Purity Test", both of which are adaptions (or ripoffs, if you're feeling cynical) of older ratings for other things. Many fandoms have their own versions of a "fan code" and a "fan purity test", although both seem to be less popular now than they were in the 1990's.
TransFan Code was adapted from the classic "Geek Code", and is not a way to encrypt messages. Rather, it is a string of letters and other characters to put in your .signature (or elsewhere, like your website) which summarizes your involvement in TransFandom. For example, the letter G is followed by a series of plusses or minuses, the number of which express your "General Love of TFs". There are more letters for MUSHing, fanfic, size of toy collection, convention attendance, and so on. To write your own code -- or to understand somebody else's -- you need to look at an instruction sheet which lists the letters and their meanings. TransFan Code was developed originally by Lizard, with the help of various members of ATT at the time of the code's first writing. Currently, the code isn't being updated, but an old version of the specs can be found at the website of the mighty Jameel.
The original Purity Test is a classic Internet document consisting of a long list of yes / no questions regarding sexuality and sexual experience intended to gauge one's "purity". It's a big joke, but it's fun to play with. In the same vein, several fandoms have created purity tests to find out just how devoted its fans are. The TF Purity Test was written by Diana Calder, and it hasn't been updated in a very long time, either, so it's pretty much a G1-only thing for now. Maybe somebody ambitious will bring it up to date.
Feel free to be proud of a high purity test score or a long TransFan code, but don't be under the illusion that it really means anything. ^_^
Complaining is something that you'll encounter in any fandom. It probably varies slightly in intensity from topic to topic, and it definitely varies within a single topic (such as Transformers) depending on what forum you're looking at. Not too surprisingly, most of the complaining is motivated by dissatisfaction with some aspect or another of Transformers or Transfandom. If people aren't happy, they'll say so. And that, in itself, is not bad. The point of gathering with other fans is to talk about Transformers, both likes and dislikes.
There are times, though, that discussion of the dislikes starts to take over and / or becomes heatedly angry and even hostile. It often reaches a level where the complainer is essentially saying that only an idiot wouldn't agree with them. And that, really, is a problem. It gets other people angry, too, either because they get caught up in the vitriol, or because they disagree and don't like being insulted. Before you know it, the whole forum is just a bunch of people yelling at each other.
Why are they getting angry in the first place? Basically, Transformers "means" something to them and they feel like the powers that be are treating the franchise with a lack of respect. I can sort of understand that -- Transformers definitely means something to me, although I don't think I could really put it into words. It's never seemed to me like something that was worth being angry about, though. Transformers is a hobby, and I get a lot of enjoyment out of it. If I thought Hasbro was doing something that would bring about an end to the franchise, I'd be bothered by it. The important thing to remember, though, is that whatever changes might occur never invalidate what has come before. If you hate everything that's been released since 1987, you still have everything that came out before that. The fact that there is more Transformers material in addition to the stuff that's dear to you... it doesn't seem like that should be a source of frustration.
Here's something that was once posted to alt.toys.transformers by a fan named Kendrick:
"As a singular entity, Transformers is not a religion. You cannot blaspheme it. Transformers is not politics. You cannot be a traitor to it. Transformers is not sacred. You cannot desecrate it. Transformers is not science. You cannot measure it or give it standards. Transformers is not dead. You cannot expect it to stop changing as long as there is a continuing fiction... or a continuing business need."
The age question used to be a lot easier to answer. For a long time, nearly all Transformers fans had grown up in the mid to late 1980s. With the wide success of the Beast TF lines, and continuing success of the newer stuff, new and younger people are joining Transfandom all the time. The distribution of ages depends a lot on which Transfans you're talking about. In the Usenet newsgroups, most fans are in their 20s or even 30s. In newer fora like the Allspark, the average age is a lot lower, with most (not all) participants being between their mid-teens and mid-twenties.
You'll find that most Transformers fans are fans of science-fiction in general, often (but definitely not always) with a particular fondness for robots and anime. They usually like video games, and many read comic books. It's difficult to get much more specific than that, though, without being inaccurate. There are widely ranging opinions on things like Pokémon, Buffy:TVS, Disney, South Park, or whatever else you can imagine. Trying to summarize would be unfair. If you're looking for people with whom to discuss your other hobbies, you should do a couple web searches to find communities set up by those fandoms. And don't be surprised if you see a few other Transfans in those other groups that you find. ^_^
Yeah, no problem. Just check the glossary (