I don’t have the CCC with me and the online version doesn’t cite the footnotes. Anyway, the way these two sentences are set together in the CCC: “it is necessary that each and every marriage act remain ordered per se to the procreation of human life.” “This particular doctrine, expounded on numerous occasions by the Magisterium, is based on the inseparable connection, established by God, which man on his own initiative may not break, between the unitive significance and the procreative significance which are both inherent to the marriage act.” Hmmm, I see it now. So it is Church teaching that the man must always intend to finish inside.
But with old people, it is NOT meant to burden than and make things feel unnatural. I would say the intention to follow the CHurch suffices, so they don’t have to worry about forcing it onto themselves in the heat of the moment