My SIL is in her mid-50s, and has no training in any field. She was a SAHM until her divorce.
Recently she completed a course to be a dental assistant. She's having a hard time finding a permanent job, but she's still looking.
Her major hurdles are:
1. She was a lot less familiar with computers, smartphones, tablets, social media, Excel, etc, than the rest of the class (which consisted of mostly kids who were 18, 19, and young 20-somethings). Of course, that's not a blanket statement about 50-somethings. Many of us in our 30s, 40s, 50s, 60s and 70s are very comfortable with computers and have excellent technical expertise. I'm just saying that because my SIL hadn't used a computer in a long, long time (decades), she wishes she had taken some computer classes prior to enrolling in the dental assistant course. My dh and I bought her a tablet because she didn't have a laptop, or smartphone, and I basically had to teach her how to use the tablet (wi-fi vs data, apps, email) from the very beginning (including how to turn it on). So that's a consideration: careers of this type require using the office software, emailing customers, using databases, operating complicated computerized equipment (my SIL has learned to enter all the patient's info into the computers, and use the computerized equipment for xrays, etc). She mentioned to me how completely different it was from when she used to take her kids to the dentist when they were little. But she learned quickly and graduated with honors!
2. Another issue is that it's not easy for my SIL to move. She isn't finding jobs in her small town, and doesn't have the money for gas to travel to a larger city for a job. If your area has lots of medical offices, or if you can travel easily, then that makes things easier. She found that the 19 and 20 year olds in the class weren't as settled down - many of them were in temporary roommate-sharing situations, or staying with friends, or didn't have families, and my SIL heard them saying things like "oh, I think I'll go stay with my aunt, she lives in a much bigger city and I can find a job there." They don't have "stuff" (a house, furniture, kids in school, etc) and it means they can just throw their backpacks in a car and go stay with friends while they job hunt. My SIL is divorced, has visitation to consider, an apartment lease - she just can't pick up and go where the jobs are. Plus she doesn't have the time to commute for a long time. Some of those younger people in the class can commute for hours - they have no one to rush home to make dinner for, put to bed, get ready for school in the morning, etc. So she's trying to find a job close to home and it's difficult.
I don't mean to discourage you - I'm just telling you the 2 roadblocks my SIL has encountered. She's considering taking a job with a temp agency. However, when she did her training near the end of her course in actual dentists' offices, she found out that every office has different software, different computer programs, and being a temp means you have to constantly be exposed to very different computerized systems and learn them fast.
She has not found that being in her mid-50s has been a deterrent. It's just the computer familiarity and not being able to travel very far (or move) to find a job have been her issues. Actually she found that being more "adult" was beneficial. There were many strict rules in her course (no artificial nails, no jewelry while in class or on duty, no long nails, hair worn in a certain way, a dress code, etc). Many of the younger students really balked at removing their ear gauges, and some acted as though their lives were going to be ruined at the horror of not being able to have their gel nails and piercings! She understood the safety aspect and complied and her instructors appreciated her maturity. Some of the younger, immature kids who dropped out seemed to think that they would just get to hang out in an office with friends, have coffee breaks, and occasionally answer the phone. When they saw the course work, they bolted for the door. Again, my SIL went into the course expecting to work hard, and her instructors appreciated that as well.
Hope this is helpful! Good luck!