What career can I begin aged 38?

Too old. The cut off I believe is 37.

Fart Garfunkel wrote:

Police officer, professional fire fighter, gym teacher, administrative assistant/secretary, auto mechanic, welder, electrician, data entry, medical billing and coding, etc.

Lots of options with little to no time or investment required to start. Think of any job that you could get straight out of high school.

The Fire department is hard to get on. It's very competitive. A lot of people with prior military service apply and get veterans preference points to help their exam scores. Bigger departments in more populated areas have a lot of applicants. A lot of them will require you to become an EMT prior to applying. It didn't use to be that way but now it is.