Thanks for your playtest feedback, that's very valuable! First of all, as per "how do I distribute the dice or die for the next age": you don't. Moving to the next age only allows you to gain new dice when a single mistake occurs dusing problem resolution. When you learn from your mistakes you can only gain new dice "up to your current age".
My solo plays were often organized in one short adventure per age, the number of scenes has always been different each time depending on how it went. For example, I have played a medieval one-shot as a daughter of a blacksmith. She was good at crafting weapons (talent 1) and selling merchandise (talent 2) and wanted to become king's blacksmith (goal). Using an oracle (Mythic GME in my case) I determined the starting situation: a chief of royal guards came into our village and I had an opportunity to ask him to become a blacksmith in royal army. This Teen memory was pretty quick: I had to prove that I was worthy by crafting a knife as a showcase of my talent (succeed craft with target difficulty 8) and afters a couple of good rolls I succeeded at my current goal. My Young Adult memory was much much longer though: oracle determined that I had to succeed at finding right materials and crafting a shield at difficulty 12. I failed a lot, each time I decided that I needed someone's help and each time it turned out to be almost a separate adventure. Each adventure provided me an item or a knowledge that I estimated to +1 bonus to a single roll, a reroll of a single die or similar bonuses (cf. "How do I hack this game?" section). After many tries, I succeeded to craft a good shield and advanced to Adult age.