How do I start a long-running game?

I discovered I was making the same sims over and over. I made my own sort of challenge. I rolled dice to get my sims traits and story. I made a list of milestones and when she reaches one I roll the die again. For example my current game was a homeless teen. She had to earn enough money to have a small house before she could get things like a bed, fridge or toilet. She had to earn an A grade, age up to young adult and have a small house before I rolled again. The next story she rolled was twin siblings. So she had to earn enough to add a second bedroom and furnish the room to gain custody of her siblings. She is trying to give her sisters the best possible life so all holidays are done with great enthusiasm. She rolled the Music aspiration next and per my rules she had to move to San Myshuno to pursue her dream.

I am having a lot of fun with this because even I do not know where the story is going to go. I hope I can keep it going for several generations. The story does not get stagnate because it is constantly changing and evolving.