I am a lawyer, so teaching English as a second language is a new career path for me. I've been out of school for a long time, too. I was probably the eldest in my class.
I took the CELTA course in 4 weeks, because my personal situation required me to take the condensed course. I wish I had taken it over a longer period to let the sheer volume of the material sink in more. It is VERY condensed, and quite demanding, and valuable.
There are two reasons I think CELTA is the premier ESL training program. First, you teach real students immediately, and second, you get thorough feedback after each & every teaching session. That's extremely important and I think it's unique to CELTA.
The trainers are grammar gurus, too. They KNOW their stuff and can articulate it well, and usually can help you figure things out for yourself (which is what we need to do for our own students, so they "walk the talk").
The only problem I faced (other than the sheer volume of information), is that there was a lot of education "jargon" which was totally new to me. Their methodology seems sound, so I trusted it even though the underlying theories were not always intuitively obvious. Also, there are a ton of different reference materials used in the course. But there's no central index, so you have to spend time looking for things that could be found more quickly with an index.
I graduated in late July, 2018. Within days of posting my ESL resume online, I had employers inquiring. I had to narrow my search down b/c I was actually getting too many inquiries. (This job search was more immediately productive than looking for a job as a lawyer, believe me). The CELTA course is more expensive than other ESL courses but I have a hard time believing the other courses are as thorough.
I signed a contract to work overseas within a month of graduation and am moving to Eastern Europe next week. I chose this particular job because they are modeled after CELTA's program so their content & approach were familiar. Also, the interview on Skype was with staff who were very warm, open and supportive. They were not recruiting so much as looking for a good fit. I didn't want to jump into a classroom without any support for my first teaching job. So that sealed the deal for me.
This career change is doing exactly what I hoped it would do. I have always wanted to live overseas, immerse myself in a new culture, and I've always wanted to teach. I leave for Poland next week, 6 weeks after graduating from CELTA.