The following questions were answered by astronomer Dr. Cathy Imhoff of the Space Telescope Science Institute.
All astronauts have some special skills, either as pilots or scientists.
So they have all gone through college and gotten some experience in their particular field. I don't know of any age requirement, but the experience that is needed would probably mean that the astronauts are at least 25, more likely over 30. I asked your question about what an astronaut wears to my friend, Ron. The EVA suits are the same with an added cooling garment that goes on over the long johns. It is like another pair of long johns with small plastic tubing woven all through it.