Not COBOL but years ago I did some work on IBM AS/400 using RPG. For those who don’t know, RPG was originally written (in 1959) for punch cards and the programs had to be written in a pattern that resembles punchcard. It was a fun experience and I am grateful to have dabbled in it.

Many megacorps still run AS/400 and it’s uptimes and performance is legendary.

Edit: Forgot to mention that I was mentored by folks more than twice my age that time.