My wife and I are in our upper 60s and our sex lives are great. We both believe that sexual intimacy is very important in a loving marriage. So much of sex is in your brain, your attitudes, your beliefs, etc. There is also a physical component. We consider ourselves very lucky as we are in love, healthy, fit and active. We are retired but keep very busy with hobbies and volunteer work, but we always make sure we reserve time for sex.
We don't have fast sex, we usually take an hour or more as it takes a long time for my wife to orgasm. I love foreplay and we take our time. I like to lightly caress her body and see and feel her respond. Yes, her breasts still do swell and tighten and her nipples get very erect. Her heavy breathing and body responses are a turn on for me too. When I move down and find her clitoris erect and her vagina very wet, she is super turned on and wants me to enter her and climax. Like most women, she doesn't orgasm from intercourse, but she likes intercourse — it is like a continuation of foreplay. (She likes me to climax first because her orgasms are very intense and she can't take me while she is in the midst of her orgasm.) After I climax I try to keep her at a plateau while I catch my breath. Then I take her to orgasm by fingers, mouth or toys. Her orgasms are like a 10.0 earthquake, and her skin is so sensitive she cannot be touched anywhere. After a minute or so she starts to "come down" and then gets another, what I call "aftershocks". This goes on for up to 10 minutes and then we can cuddle and doze off in each other's arms.
We have sex 2 to 3 times a week. We usually have a Sunday afternoon date in bed, a Wednesday morning wake-up sex session, and any other time the mood strikes us. Like yesterday, I woke up at 4:30 to go to the bathroom and when I got back to bed I wasn't sleepy. I started lightly caressing her and in a couple of minutes she was breathing heavily and very welcoming. At about 5:30 we went back to sleep in each other's arms. She was smiling sensually all day.
We always had a great sex life, and things did slow down a bit 4-5 years ago. My wife was concerned because she wasn't initiating sex quite as often as me. Then she saw an Oprah series on bio-identical hormone replacement. It is not only for sex, but for energy, aches and pains, and all that getting older stuff. She tried it, liked it, and then we both started treatments. It is great! You have more energy, the aches & pains of an active life are gone, and your libido goes back to where it was in your 30s.
The bottom line for us is, you can do things to "stay young" and sex is a vital part of staying young and in love.