Hi Lulu and welcome to the site! It's great to have you here.
I've wondered a lot (actually read: worried myself crazy) about loose skin too - I have about 150lbs to lose in total. However, there have been threads about this before and from what I've seen, no one has experienced any problems with it - with the exception of those who's skin has lost some elasticity due to things such as preganancy(ies). I think Nancy meantioned that she had a little arm skin after she lost her weight but it did firm up over time. My brain is like a sieve sometimes but I think she said it took about a year for it to settle. (Please correct me if I'm wrong!)
I have to keep reminding myself that this is NOT like gastric bypass surgery where you're dropping 15lbs a week. It's faster than most other diets, but not so fast that your body freaks out.
I'm pretty confident in saying that one of the most important keys in retaining skin elasticity is hydration - i.e. ensure that you are drinking at least 64oz of water every single day. I've also heard that shea butter and cocoa butter can help skin a lot. I use them like its going out of style and *cross fingers* I don't have a single stretch mark.
As a side note, if anyone does have any fresh stretch marks (the ones that are purple/pink in color) try Mederma. My mom bought me some for a scar after she used it on one she had and it makes a HUGE difference! The packaging states that it can be used to fade stretch marks and make them appear lighter and softer, so I thought I'd throw that out there. (It will not work on old white ones).
Anyway, I hope you found this helpful.
I wish you every success!
Alisha