Fitness for fun(ction) and disliking exercise

Not having to exercise much is a luxury I've always had, until recently. In the past I played sports, had physically demanding jobs, or did just enough hiking, kayaking, and push-ups to stay around my target. I understood, but never identified with, people who had to buy a gym membership and punish themselves daily on a treadmill or weight machine to stay in-shape. It seemed excessive wasting (in my estimation) hours a week, thousands of hours a lifetime, doing something that allows one to live that much longer, particularly if you find fitness unenjoyably. Then I started getting old.

My wife and I recently went on a cruise that offered a rock wall. I got to the top fine on "easy" but struggled at harder levels. My arms gave out looking for holds on a difficulty that would have formerly been easy. It made me realize that without regular self-testing, my actual ability had decreased while my perception of my ability remained the same. It's like when someone's "eyes are bigger than their stomach". I had an over-inflated perspective of my own ability based on past achievements. I put on rollerblades and look clumsy jumping a curb when I used to jump stairways. I get winded after jogging a mile when I used to break track records.
Surely, this is a regular realization for someone my age, as is the exercise that follows, but as mentioned, I don't particularly like exercising. This dislike keeps me from sticking to long-term fitness goals. I convince myself that mediocre health is better than the torture of a personal trainer or a gym.

The solution that has been working great for the past couple months is what I'm calling functional fitness. I want to be able to survive a zombie apocolypse (or at least participate in a 5K zombie run). I want to be able to rock climb with ease (or at least climb all the difficulty levels on a cruise). I want to be able to chase down a purse snatcher or outrun a calamity. I don't want to watch myself grow slower and weaker with age and eventually realize that the limits of my ability are a short walk around the block or that I can't even ride a motorcycle without being sore. I'm not fighting death, it will come. I'm fighting because I want to keep or win back thee things I enjoy doing and want to be able to do them for as long as possible.