I am 58, dating, partially impotent. I usually date women 45 to about 60. When am I obligated to tell them?

Do most women in my age range still want ? The women I date are fairly traditional and not into early or promiscuous , so I can put off telling them for awhile. But I want to be fair to them. I said "partially impotent" earlier because I think I can perform in some rare situations, but not often and not without physical help from a woman. Do you think women my age are willing to receive from a man in my situation as a substitute for the real thing? Any ideas will be appreciated.