Hmm, I'm getting married next year as well, but my experience seems really different.
I'm still nervous about it, but none of those issues seem to be present for me.
My fiancee is pretty independent (like myself), already makes good money (together, we'll be doing very very well), respects privacy (and I respect hers), never places blame where it isn't due (I'm lucky here), and that's not even touching on everything I love about her.
Still, I too have been on my own for years and it's going to be very strange having someone else under the same roof again. The marriage ceremony itself seems like it will be pretty difficult to setup, though (getting married in her hometown in France). We're making good progress, but there are a lot of things to complete. Fortunately, she's not really a bridezilla and, while the wedding is very important to her, her view seems a bit more down to earth.
I do think marrying a young girl (20 year old, like the OP mentioned) seems a lot riskier, though.