Pentesting is best learned by doing more than anything else. Using the CEH example specifically, you could study and pass that in a week, and that's being generous. I did it in about three days at the beginning of my career knowing fuckall about pentesting. It's an insultingly easy cert to get and the questions are stupid easy enough to even guess the majority of them. Truthfully, I would avoid using any sort of cert (yes, including the OSCP) as a gauge for "getting good" at pentesting. If your goal is to just learn about pentesting, save the money all around and go for the CPTS from HackTheBox or the PNPT by TCM security. Sure, they don't have the "reputation" of the OSCP but frankly the OSCP has (in my personal opinion) rapidly become a ripoff for what you spend vs what you get.