Sex seems (and is) pretty effortless, most of the time, when you are young. (Though, of course, if a couple makes lovemaking an athletic event, that might require effort.) As our bodies age, though, even the physical effort to make love can be more demanding. And the emotional work can be more challenging as well.
When you have made love to your wife for many, many years, marital sex tends not to be quite as spontaneous as it was when you were young, unsurprisingly. Perhaps even more than earlier in marriage, marital intimacy needs to be prepared by extensive conversation, to create the sense of closeness that women, in particular, often need before engaging in marital sex.
And then, even after this conversation and the accompanying embraces, it may take longer foreplay before she gets in the mood and is prepared for sex. Again, it’s unsurprising that what you’ve done a thousand times before in foreplay doesn’t have quite the same desired effect of arousing her (or you) as quickly. Sometimes one can kiss a wife or fondle her breasts for an extended time, and it doesn’t really move her much. Even the physically most stimulating foreplay (at least for many women) – what I call “glossing” (oral foreplay) – may take longer to arouse her. (Of course, taking longer can sometimes be nice! And slow can be good.)
Then, there are the moments when a couple changes positions, either slightly or greatly. They might be lying on their sides facing each other and kissing in a close embrace, and the wife might want to shift on to her back (if she prefers having her breasts kissed in that position, for example). When you are older, something as simple as that can turn out to be not quite so simple as it once was. Turning the bodies and getting them re-settled may take a little time and produce a bit of discomfort in the process, which delays getting back on track, moving forward in the act.
Another challenge can be when we’ve had an embrace for a while and then go to change positions and our skins “stick” as we move. Ouch! – that can hurt! Being careful about changing positions may be essential for old people in a way that young people would never give a second thought to.

So, older sex can be hard work. The physical challenges of older sex may even affect how often the couple does it. But it’s still so worthwhile. Above all, it does help reinforce and deepen the connection or bond between a husband and wife. (That is, after all, a key part of what it does – with help from that wonderful oxytocin!) So, we should just adapt to deal with the physical challenges, (e.g., go slower, be more careful) and continue to enjoy this wonderful gift we share with our spouse.