I think any time is a good time to start. "Now" is even better. I might start again tomorrow or the next day.
For me, the motivation that is the strongest is when I decide to lose weight, exercise more and eat healthier for me, because I want to do it for my own health. My wife can encourage, the Dr. can make all kinds of suggestions, but until I set it in my mind to do it because I want to do it for me, it does not really happen. I do try fairly regularly, and have had some success in walking and losing weight, but do know I have to get back to being more serious about it.
The mind set that I am trying to get better for my own sake is a strong motivator, and in doing so it makes things better for my wife when I am healthier too.
Not sure that makes a lot of sense, but main thing I am trying to pass along is make sure you keep reminding yourself that healthy is good for you.