You can check the actual date (and time!) you joined AB, simply by clicking on 'my profile'.
Public profiles have been suggested before but the AB team never seem to like the idea. One problem with public profiles, of course, is that they rarely tell the truth! I've got dozens of 'profiles', all over the internet, and not one of them is remotely accurate!
Now that the 'no e-mail addresses' rule has been lifted, it's simple enough to invite another ABer to make contact, just by putting an e-mail address in a post. (I normally create a different address every time I do this. If I start getting spam to a particular address, which is only used for correspondence with one person, it's easy to switch to a different address).
I started some e-mail correspondence with another ABer last year by inviting him to contact me. He was in Colorado and about to visit the UK for the first time. I ended up meeting him at Waterloo International, so that I could give him a guided tour of Paris!
Chris