Two big considerations for motivation. (1) If you can see results you'll stay motivated. Weights are great for this, though less so for an older body. Give them 2-3 weeks, and they've got you. (2) But, during plateau and low energy periods, as well as time constraint days, having to drag yourself to the gym is a major disincentive.
I combined lifting with various sports for 45 years, and got a nice collection of injuries as a result. The last two years I've been doing a self-concocted version of the old Charles Atlas dynamic tension, which is basically using one arm or leg to provide the resistance for the other. You can work the muscles from various angles, not just the one that the lift allows, and work around any muscular injuries. The results for me: This routine doesn't bulk you up as much as weights, but you stay strong looking and have more definition in the arms. It's a physique that may well be appealing to more female eyes than the jacked-up lifter look.
You can knock some of these out in 10-15 minutes anywhere, and keep the demotivation monster on its leash without the need to invoke massive will power.
Check out the website transformetrics and its living strength forum. It's roughly 20 guys and their guru, who is in phenomenal shape at 64. They bat around various theories of these old fashioned "physical culture" forms of exercise, and the guru produces books. He's been working on his ultimate magnum opus for some time now. One theory he has talked about re Sanford Bennett, "the man who grew young," is the possibility that just flexing all your muscles in some fashion every day releases growth hormone and keeps you young.
My website is currently in suspension until I can pay extortion money to the malicious techie (in my employ) who first shut it down, then screwed it up. But such as it is at the moment:
http://www.geographyofhealth.com.