Oh, and size doesn't have any effect. Some 4 pound 34 weekers will do better born early than a 7 pound 37 weeker. That's why the amnio is needed. I have heard that girls tend to reach lung maturity earlier than boys, but I don't remember where I read that so I'm not sure how accurate it is.
My step sister had an amnio done once a week starting at 34 weeks to check lung maturity. She was having a second c-section 11 months after her first one and also had placenta previa for a second time. The test at 36 weeks showed baby's lungs were mature and she delivered her with absolutely no issues. It depends on baby, but 36 weeks is possible, and it's good you'll be able to know before your c-section.
They're usually mature @ 37 weeks but you're real close so I'm sure your baby is very close if not already matured, gud luck!
It's hard to say for sure. I'm assuming they are doing an amnio? That's a really good thing as if lungs are not mature they can give you steroids to help the process along. In any event, no worries at all. They will take good care of you and your little one, and at almost 36 weeks baby will be just fine! Sorry you are going through placenta preva, but it sounds like your Dr.'s are doing their due diligence and that you are in great hands.