Well, there's Pam's brilliant Hearts Divided (which has a sequel, Hearts United that I still need to finish reading. Bad me!). It's a bit of an elseworlds, but definitly fits the first criteria.
And I'd like to say there's at least one more, but I can't think of it for the moment.
I can't think of any that meet both criteria, either. But Jenni Debbage's first Universal Union has Kal El coming to earth as an adult. (think he was nineteen )