Hello and welcome!
It is completely normal for bodies to change through different age phases, medical phases, or life changes. As people age, they tend to lose lean muscle mass and gain fat mass, which results in the body burning fewer calories. Regular exercise as approved by a doctor can help with this, but some metabolism slowing is expected. Diet changes can be required for pregnancy, aging, health changes, activity changes, and any other number of things. It's just about realizing it and then taking action, which is exactly what you are doing, so congrats!
That being said, it is completely possible to lose weight at your age or older. I have a friend who recently went from 165 to 130 in a healthy, steady manner. She's your height and is 65 years old. She did it basically through portion control with some calorie counting (to get an idea of what an actual portion is), and no exercise at all. Even at 165, she wasn't 'pigging out,' but it was still too much for her body. So she adjusted. She tells me she feels great now.
There's a lot of information on this site that can help you figure out what you want to do to lose weight. I recommend looking at some of the active threads (there are a few floating around) to talk to some people, and also check out the archives of old threads. There's some good stuff there.
Welcome again!