Nearholmer - that graph is pretty frightening, but then any trip to a swimming pool on a Saturday morning will bear that out.
I have heard this too, and I think it's the case through most of life. Traditionally the BMI (which is a crude measurement, and quite inaccurate for outliers like me) healthy range has been 19-25, but it was later revised up to 20-26.5, if memory serves.
My father in law (who turned 76 today) is active and in quite good health, but he is far too thin, and you can see that he has been sarcopenic (losing muscle mass) for some years now. I've given both him and my mother in law an introductory resistance band training program and a suggestion to eat a little more protein and a little less cake!
On the topic of BMI and muscle mass, BMI gives no indication of body composition. You can be within the healthy weight range and deeply (metabolically) unhealthy.
The key is to build and sustain a healthy amount of muscle. It's highly effective at preventing type 2 diabetes and other metabolic issues. Given that falls resulting from frailty in later life are often fatal, having strong muscles is vital.
I remember seeing this photo set years ago and considering how remarkable it was. There is little to no difference in the leg composition of a 70 year old triathlete and a 40 year old triathlete. And then compare it to that of a 74 year old sedentary man
