On consideration I think the real issue is health. How good is it? Are you OK with walking the distances you want to over the terrain you wish to walk? Do you have a health condition that could result in death in the wild which could be easily treated in civilization? Do you have unstable angina? Do your blood sugars plummet with exercise?
Being out of shape need not be a reason to give up the sport as long as your health permits. Just be honest with yourself and your companion.