As you get older it becomes a greater battle between pack weight and comfort. It's important to reduce pack weight to make it easier on your body while hiking yet it's also important to sleep and eat good plus be comfortsble in various weather conditions. In the past my standard pack weight was 40-45 lbs but now into my 70s I'm experimenting with a lighter sleeping bag and pack, among other things. One of the big problems is food. I take freeze dried dinners but breakfast/lunch/snacks add much to the weight. There's no one right answer since each individual is different. My usual objective is to find a nice destination, such as a lake or creek, within a 5 mi range that has some dayhike opportinities and stay there 3 or 4 nights. Most of my trips have been solo over the years and the love of being out there almost eleminates any fears I have. If you go alone, especially at our age, I would recommend you carry a Personal Locator Beacon of some kind. I also recommend bear spray if you're concerned about animals.
I too have had back problems (herniated disc/arthritis) but through exercises it's been almost eleminated as a problem.