Not too dissimilar from most diagnosis stories, I imagine...
I was 27 (and a half), when I was diagnosed.
I have some random auto-immune thing (makes me randomly breakout in hives, or get a welt here/there - sometimes there's a swollen lip or tongue) which I keep in-check with a fist-full of antihistamines every day. Nothing major and easy enough to keep under control. In hindsight, it could have been a precursor, but the reason I mention it is because the type of antihistamines, in the doses I take, can give you a little dry-mouth.
So it's Australia Day (2013-ish). I'm feeling about the same I have been for a couple weeks now. The additional pee-breaks are a result of the additional water I've been drinking which is a result of the dry-mouth from the antihistamines, is my thinking. Logical. Cause-and-effect. Occam's razor. Nothing unusual.
The day before, I'd been to the GP for a sick-day certificate (chucked a sickie from work) and thought 'what the heck? may as well get some bloodwork done - it's been a while - and get a fasting glucose test as I haven't had anything to eat this morning, by chance.'
"OK, but there's no chance you have diabetes" the GP said. "You're fit, healthy, 27, and no family history" he said.
And I left it at that. Didn't give it another thought, until the next day. Australia day (which is a public holiday, nation-wide). I got a call from the GP. He told me to go into Hospital immediately. "You have diabetes" he said.
The story from there is the same for all of us, I'd imagine. A whirlwind of new information, diabetes paraphernalia, what you can do, what you can't eat, how life's going to change etc.
Looking back, there were signs. The dry mouth. That diet I happened to be on before being diagnosed, probably wasn't the real reason for my seemingly effortless weight-loss. My vision (I already wore glasses for years before) was changing a little - I noticed that occasionally my sight would actually be better without wearing my glasses - probably because the vessels in my eyes were squeezing things back into focus?!
But, I was ignorant. Knew nothing about diabetes, and everything was innocuous enough that it could be explained by normal life. Hindsight... Watch for the signs. Have regular checkups, blood work, and physicals. You might catch something manageable, like diabetes, a little earlier, or something far worse before it's too late.