Most production COBOL programs run on IBM compatible mainframes so you'd also need to get a handle on developing in MVS aka "z/OS" and how to hack JCL config scripts--the horror! That's difficult to do without getting hands-on experience.

As someone whose first job out of uni almost 20 years ago was in a mainframe environment, I have no desire whatsoever to go back to it and would strongly recommend against working in COBOL if you can make a living using tech that was developed in the last 40 years.

Also, nobody calls it the "mainframe". It's the "host environment". It took me a couple of weeks on my current project to work out why my new colleagues were so reluctant to modify the customer re-contact batch process - "oh, that's on the host environment!".

A few years ago I landed my first programming job as a COBOL programmer, I had no professional(programming) experience or a college degree but the company offered an in-house training type deal. It was several weeks long and they had a trainer come in every day and teach us COBOL and it's accompanying technologies(SQL,JCL,REXX), the pay was 50,000 a year starting out and it wasn't a bad gig. Would I go back to it? Probably not, but you can certainly make a decent living getting into COBOL these days. The work was boring and nothing cool or cutting edge but at the time employment was employment to me. My resume is online and I certainly get my fair share of offers for COBOL work. So learning it could certainly have some merit if you're looking to make some money.

I know people that make a very good living at it. But, like anything, you have to find the 'nice' positions, and that comes from knowing something critical to a business that almost no one else knows. You can name your price then. But that usually means you spend 20 years grinding, industry and everyone moved along, and you stuck it out.

I don't think there is an advantage in general - the mean salary is probably going to be lower compared to enterprise Java, just the tails on the COBOL jobs can be lucrative. I don't think it is particularly satisfying intellectually, but that might be my bias (I don't enjoy digging through reams of code to try to figure out how to glue things together - it is a challenge).

I did my time on big iron and JCL - Do. Not. Want. Of course, these days a human is probably not walking your stack of tapes to the tape readers so you can find out you have something misconfigured .... Sometimes I'd get 2, maybe three runs a a day if the operator was really spritely!