Overall a sedentary lifestyle has worse long term health risks than being slightly overweight. The worst effects tend to show up as you age. There's a hidden epidemic of sarcopenia among the elderly.

In my understanding you don't start with a "full health" and lose it over time, instead you can always get better or worse from the position you are in. So while you won't have some dramatic problems, you'll be missing out on how good you could feel all this time.

While what you’ve said is true (according to my understanding), the older you get the more difficult it is to move the needle. It’s much easier to get into better health when you are 20 than it is when you are 60.

Also the margin for error gets much more narrow as you age.

For women there is an issue of having low bone density that cannot be fixed after the mid twenties IIRC from reading an exercise physiology textbook. Your aerobic capacity that can be seen as an approximate proxy for general physical health can be maximized by your thirties and can stay close to that with maintenance until your 70's and beyond.

It’s definitely not good. Having a healthy weight means that exercising should come easy for you. And it’ll protect you from cardiovascular diseases, enhance your mood, boost your endorphins and sex hormones and turn you from skinny to toned.