I worked as a cobol dev in my first fulltime job. I did mostly cobol85 (microfocus) and object-cobol (netexpress/fujitsu cobol), with isam files. Did the whole "migrate to year 2000" process in a couple of big but old applications (healthcare management software and manufacturing management software). Cobol is a school by itself; there are so many ways you can shoot yourself in the foot that one either learn how to structure programs avoid a spaguetti mess, or slowly descend into madness trying to fix bugs :)