Ok, you start a game just like any other and go into Create A Sim. In the lower left corner is a large button with a bunch of heads on it called Pre-Made Sims. Click on it and you'll get a window with many Sims, including ones that you've saved to the bin. You can sort them by gender and age. I originally had Bubblegum as an elder because that's what she was when I saved her. So, I found her under elders and pulled her up. Once she was on the platform, I could change anything, including her age. I made all the Dreamweavers young adults again that way.