Wow.
I'm an over-40 very new musician (in fact, 2 months ago I wouldn't have used that term) who started by picking up a bodhran and a year later stepped on my wife's penny whistle, thereby inheriting it (hence the pen name). Went from no keys to fixed key. Ignored sharps and flats on sheet music and never played along with anyone to be in or out of key with. (Hell, I didn't know what a key was - the whistle just came that way.)
Well, a year ago my family got me a small hammered dulcimer (12/11). This is such a perfect instrument to learn basic chord structure due to the string layout making it all visual.
Now I've been torturing my guitar/mandolin/bass playing brothers turning family get togethers into sessions where I try to get them to figure out what the chord progression is so I can attempt to play along (they usually haven't thought about what the chords are for years on most songs).
I came to this thread because just this week the concept of 'key' finally clicked. My brothers would tell me what key they were in (and I'd just quietly drone on that major chord). New after spending half an hour with a music dictionary (and pestering my multi-instrumentalist daughter into reading key signatures for me!) I think I've got the concept down - the key is the set of notes (specifically sharps and flats) that sound good together.
Last weekend I bought a small notebook and copied out the basic keys and their corresponding scale. Next time my brother tell me the key, I at least know the right sharps and flats while I try to figure out the chords. Meanwhile I keep on droning along...
Bent