Changing careers at 18 years into a job, is it realistic? - any advice?

After 18 years as an accounts payable clerk I am thinking about moving into a different field. I would rather hear the honest version than the polite one. I have a little time and a small budget for training. How did you start?

I began with informational chats, then a short online course, then a related entry-level role. It took about 14 months.