In general, you have to be the best of the best at something or the best at a bunch of somethings. Most astronauts start as test pilots or scientists. Almost all have advanced degrees in a relevant field.

I'm sure the path to astronaut will change a bit as many of the future astronauts will be flying for private companies, rather than for NASA, but one thing won't change. It will continue to be very expensive to launch a mission, and there will be a ton of people who would love to go, so the competition for the job will continue to be fierce.

Good luck!