If it makes you feel any better at all, I have stretch marks too (on my stomach around my belly button, on my hips, my inner thighs, and on my chest).
I have lost weight fairly slowly (I'm averaging about 1.75 lbs./week) and I have to say that the stretch marks are becoming less noticeable. They're still there, but they're getting lighter and lighter - from a noticeable pinkish/white to a duller white, more "skin tone-like" color. The ones on my tummy in particular are barely-there anymore (They were, however, also the last to form -- I got them within the past year when I ballooned up 15 lbs. in a couple months)
I expect it will take a long time for them to completely go away, but I am encouraged that they are definitely "less there" -- you're even younger than me (I'm 27), but I hope it gives you some hope! They do eventually go away over time, especially the younger you are. And if you lose slowly enough, the saggy skin should be minimal.
Female, 31 years old, 5'4 1/2" tall
Starting weight 1/4/11 = 215.2 lbs.
Weight 10/22/14 = 175.0 (net: -40.2)
Last mini-goal: 175 lbs. REACHED 10/22/14 --REWARD: New wallet
Current min-goal: 170 lbs.
Next large goal: 165 lbs. by 12/25/2014
Lowest weight: 156.7 lbs.
150.2 lbs. <--- Official "Healthy BMI" weight
Estimated final goal: 130-140 lbs.
"You don't have to change your life today. You only need to change your day today."