It may be far in the future, but there's some kind of logical way to get from where we are to where the science fiction is.

Hard to be a physics major at Rice University if you have flunked calculus.

I love biomedical science, I love astronomy, and you can't really do much with those in a fantasy setting.

One thing nobody can do better than you is be you.

There are relatively few science fiction or fantasy books with the main character being an old person.

Other people, including me, have written books with main characters who were old and rich. Or old and brilliant. Old sages, old wizards, old rich people.

When I was starting out, I did not do short fiction well, because I kept wanting to write books.