Similar story to you. Diagnosed 2010, but suspect I've had it years longer.
Thanks to the wonders of technology, I found e-mail correspondence going back years, in which I'd said to friends things like: "I don't feel very well", and: "I think there might be something wrong with me."
And I'd had inconclusive hospital investigations at least four years before diagnosis, too. I first saw a consultant rheumatologist, who was convinced something was wrong. I was optimistic he'd get to the bottom of it, but when I went back for my follow-up, I discovered he'd left. His successor diagnosed "wear and tear" ("Unfortunate, at your age, but it does happen") and discharged me, with advice to "rest and take ibuprofen".
Resting and taking ibuprofen didn't really seem to help much (Strange, that, eh?), but I naively assumed anything serious would have been found.
So I was actually comforted by the fact I'd been discharged, and did my best to ignore symptoms, after that, thinking they were a natural part of getting older.
Then, in Jan 2010, I had stroke-like symptoms, that were much less easy to ignore - completely lost sensation in my feet. This set me on the path to a correct diagnosis.
Oh, and I haven't even talked about all the incorrect diagnoses, apart from "wear and tear", such as: "It's your shoes!" and: "You have one leg longer than the other!" Complete tosh, of course. I'd never worn extreme high heels - nothing to cause me trouble walking - and although none of us is perfectly symmetrical, I'm sure I'm not so lopsided as for that to be the cause of everything.
With hindsight, it's really quite alarming the hogwash (some) medical professionals tell you, when what they really mean is: "I've no idea". At times, I've actually come home thinking it was MY FAULT, from years of wearing unsuitable shoes etc. And of course, such answers put me off searching for the real reason, because if someone in a white coat tells you: "Your problems are due to your footwear", or: "It's just your age", you believe them.
I now think there were even things in my 20s that weren't quite right. Or even before that, to childhood? Why couldn't I skip, hop, and balance, like other kids?
To some extent, I feel I've always been "athletically challenged", shall we say. But whether this is coincidence, or means things started very young indeed, I suppose I'll never know.