gwenevyn, good question. I wish I knew the answer too! I think, because I supposedly have an air of innocence (or total stupid oblivion? unknown), some individual(s) feel the need to offer 'advice' or their unwarranted opinion. Although sometimes they may be well meaning, I suspect there is a touch of self-righteousness underlying. I think what you said, in paraphrase, about just honestly saying in brief, "Please, I don't need/want to talk about this any longer," may be the best approach. Ideally, anyone would understand this means 'stand down' but with certain advice givers they almost need a hard whack over the head to stop! (Don't do this though)!
Do you think a heartfelt sincere note, just stating, in effect, 'Whilst I appreciate your effort/concern, I do not feel the need for advice or assistance at this time. If this should change in the future, I'll say so. Otherwise, please respect my preferences." Then, if/when well-meaning advice giver starts, just remind them of The Note.
Even though this unwanted advice could be irritating, resist the urge to throw a tantrum - just makes it worse.
<Secretly, get a voodoo doll to take out the stress> Good luck gwenevyn....I hope no one 'talks down to you!' I think intent is everything here.
_________________
The ones who say “You can’t” and “You won’t” are probably the ones scared that you will. - Unknown