If you get far enough away from these two notions, it is possible to imagine them as binary. You are old or not; you are active or not. When you get closer, it seems more reasonable to ask things like “how old” (not numerically) and “how active.” In this essay, I would like to take one further step in.
“Old age,” it is often said, is a matter of attitude. I think there is a small truth buried in there, but it isn’t very big and it is deeply buried. Attitude can be important if you use it as an excuse for not doing what you are capable of. Of course, anything can be used as that kind of excuse, but “I’m old, you know”  is particularly vulnerable to misuse. On the other hand, “old age” can be seen as a motivation. When you see old people living with abandon, utterly unconcerned about their calendar age and not even entirely prudent about their physical condition, you might be genuinely attracted to it and say, “I could do that.”
But mostly, when I think of old age as an attitude, I think of people who have given up on living and are just putting in the time until they die, the way we used to put in school time until we were allowed to go home. Those people, of whatever age or physical condition, are old.
And most often, not always, they are inactive.
But there are old people who drive themselves to a lot of physical activity, taking no joy in it at all. Their activity might better be called a way of dying than a way of living. It is just another way to fill up time.
It doesn’t have to be that way, at least it doesn’t for most of us. I began, some years ago to distinguish between “me,” myself, and “it,” my body, or, more concisely, between “myself” and “my self.” Again, for practical purposes only, I will say that “it” will die and “I” will not. What you get for being willing to make a distinction of this kind is “rising above decline.” 
This means that “it” will decline. Period. I, watching from the stands, can be alternately amused, disheartened, encouraged, and so on. That means I can be as active as my body will allow and to do it as a way of living, not as a way of putting in time until I die. “Old and active” is that kind of combination.
Of course, it is true that the more your body will do for you, the more active you can be. I sorely miss running on the trails in Forest Park, but the fact is that I can’t run anymore. I have taking to bicycling, which I enjoy (but not as much as running) but there will be a time when bicycling is no longer safe for me. If I am old and active, as I propose here, I will take the next activity down, whatever it turns out to be, and do it as fully and with as much enjoyment as I can.
The alternative, of course, is not refusing to age. “It,” my body, is going to continue to decline, but if I am getting out of it all it is capable of giving, then I am doing it right. And if I live with appreciation and satisfaction and maybe just a little daring, then I am doing that part right too.
It’s a challenge, but it’s too good a chance to pass up.
 I devised a category of such people, IOYKers, in a previous essay
 I know that sounds like the very worst kind of dualism (I mean the Cartesian kind), but I mean it kindly. I do understand that we are, in fact, a single psychosomatic unity.
 Which I came across as a report on unused school space in Boston. I didn’t find a use for the report, but I fell instantly in love with the title.