Well I don't know. As i've stated in a few different threads, i went from 220 after pregnancy to now very fit and bodybuilding. I literally have almost *no* skin. If I lean over and look at my lower abs, I have faint stretch mark scars like way low, just above my pubic bone, and the skin is every so slightly not as tight as the rest of me. I'm working on getting my body fat down and putting on a few more pounds of muscle and my trainer thinks it will shape up the rest of the way. I want to see some skin, I can show you some LOL, i'm not joking about how much i weighed. It CAN be done. Sure sometimes there are just times you will have a little skin, but usually it's in a place covered by bikini underwear and doesn't need to sag!! It depends how hard you work. I am really inspired at my gym to talk to mothers getting in shape because I HAVE been there! I changed my routine so i have one day of intense core training, and I'm expecting this to shape up my mid section further so I can see my ab muscles better.
It depends how determined you are. The problem is you cannot "fix" ONE area of your body. You have to work at all of it. You can work your core section harder to build strong muscles and that WILL help a lot. IT's kind of joked about here all the bodily issues that come with motherhood, but I'm really serious about fitness. It depends on the individual's goal. I don't think there is anything wrong with NOT caring about being in perfect shape or working out hard, but it's also not vein or wrong to look the best you can if THAT is your goal, you know? I think everyone is beautiful no matter what their looks, but for me body building is a hobby