Can endometriosis cause infertility in a 20 year old?

Yes. Endometriosis is one of the major causes of infertility, so the answer to your question is "yes".
Endo Infertility? Endometriosis is associated with infertility but many women with endometriosis have no fertility problems. We grade endometriosis from minimal to severe. The more endometriosis the more likely that it actually causes infertility. At your age, the chances of success is very high. See a fertility specialist if not pregnant in 1 year of well-timed attempts. Best wishes.
Endometriosis. Endometriosis is associated with infertility at any age. Not everyone with endometriosis is infertile. The younger you are then the more likely that you will get pregnant with or without help. The more endometriosis then the more likely that you will have fertility problems. Repeat surgery is not very helpful for fertility. At age 20, you should be very optimistic but don't wait too long to try.