Usually, 18 with a High School Diploma or GED, will get you in the door in T&E, MoW, or Mechanical.
To be a supervisor, you need a bachelor’s degree or the equivalent experience. In you have no RR experiance, you’ll need a bachelor’s. Most Class I’s are tending towards making a bachelor’s a requirement, for any position higher then trainmaster, even with a deep RR background.
If you work for a Class I, the pay is OK, but you have next to no time off - one day out of seven, but working 14 or more days straight is not uncommon.