Yes, the dreaded weight gain around the mid-section - it happens to the best of us, at about the same age as your sibling. This weight is hard to lose. Actually my husband who weighs 168 lbs. went from a 34 waist to a 35 at age 60 and was told he was "obese". Really? How can you possibly be obese at 6 ft. and 168 lbs.? It was the BMI.
I have seen women whose weight did not fluctuate more than 5 lbs. but there was a redistribution of weight and many could no longer do up their zippers etc. They exercised and starved themselves to know avail. Some did lose the 5 lbs. but the redistribution of weight was still there. Build has a lot to do with it as well. Actually I have this issue as well - also I look thinner than I am based on build and the way I dress.
Forty lbs. is a lot - but I do not think your sibling will be able to lose all of it, considering where it is and his/her age. Frankly though when I lost weight it was my decision. We each have our own trigger that will ultimately cause us to lose weight. I obviously came face to face with mine, and it was not health related. Many people who do have to lose weight due to a specific health risk unfortunately do not do so either.
I do hope your sibling manages to lose some of the weight. It can result in heart issues. If my doctor told me to lose weight for a specific condition I would do my best to follow her advice. I would be too afraid not to (more so of her than the health risk I am sorry to say - and she is a great doctor with a closed practice).