Yes, you did understand the meaning of “impotent”. Impotence is NOT sterility–one can be pretty “potent” yet be incapable of conceiving a child.
Impotence means that one cannot engage in genital sexual relations (hope that isn’t too graphic). While it might seem harsh to say that those who are physically incapable of the marital act (while they might have perfectly fine sperm counts or perfectly working uteruses/Fallopian tube etc.) cannot be VALIDLY married (after all, they usually aren’t DELIBERATELY impotent, are they?), it goes down to the “procreative” and “generative” aspects of marriage.
Marriage isn’t just a “civil covenant” where two people who love each other sign papers, have a ceremony, and then live however they please.
Marriage is a sacrament, instituted by God, and it has both certain rights and certain responsibilities.
God isn’t an old meanie who unfairly first creates somebody “impotent” and then further dumps on him (or her) by saying, “And you can’t get married EITHER” as some great cosmic and undeserved punishment–but I’m sure that is the secular humanistic view, which simultaneously raises “love” as THE ONLY REASON for marriage, ignoring spirit and God, while relegating “conjugal” love to influence by contraception, abortion, and “same sex” marriages which of course are both sterile AND impotent and making them “add ons” to the one blinding “we’re in LOVE, therefore we DESERVE marriage” concept so prevalent today.
God has given us all a specific “purpose” in life. And He’s given us our specific “crosses”. NONE of those crosses is unbearable, since God does not hold us to impossibilities (same as He doesn’t bother with silly problems of “shall I make a rock too heavy for Me to lift” and other ridiculousities). Some of those crosses, depending on all sorts of factors (today, very heavily influenced by a secular and antireligious society), are heavier than others TO A GIVEN PERSON; however, the rewards are greater as well.
“To whom much has been given, much will be demanded”.
I don’t think that we want to encourage an idea of relative “merits” of personal crosses. I imagine that the cross of martyrdom which was given to so many in the early years of the church doesn’t look so “bad” to us as the cross of SSA looks today–but we really are in very little danger at present of suffering martyrdom, while SSA is trumpeted all over as affecting millions of people, and given the full “violins and roses” treatment. “Comparison” of crosses is NOT the way to go–compassion, love, help to bear the cross, patient resignation to God’s will and prayer is.