score:4
No it is not necessarily a sin.
Babies and Bonding is a euphamism for the procreative and unitive nature of the conjugal act.
St. Pope John Paul II devotes a large portion of his famous work "Love and Responsibility" to understanding the word "To Use" and it all comes down to whether or not one or both of the spouses is using one another. If you can conceive of a scenario where it seems like a man is using his wife or a woman is using her husband in youth or old age then, that would be sinful.
distinguo Marriage itself, requires the husband and wife to have "openness to children", an infertile man marrying an fertile woman deprives her of her fertility and vice versa. It could be a matter of age or injury, in the case of age it could be obvious - as in the case of the French Prime Minister Emmanuel Macron and his wife - this kind of union should not be allowed to take place in the Church. But infertile spouses do not deprive each other of anything and therefore "openness to children" might take another course.
It must not be forgotten however that, even when procreation is not possible, conjugal life does not for this reason lose its value. Physical sterility in fact can be for spouses the occasion for other important services to the life of the human person, for example, adoption, various forms of educational work, and assistance to other families and to poor or handicapped children.
The same can be said of couples where one of the spouses did not know they were infertile, they're not intentionally depriving their spouse of children and likewise, they're not sinning when they make use of the conjugal act, so long as the are not using in the negative sense, their spouse.