General

This reminds me of the web model Boberry. She is almost 600 pounds, but is amazingly active and agile, can give a piggyback ride to another person, and can kick higher than her head. Many slim people would struggle with such things.

Obesity, like many other things, is a risk factor. No guarantee, but changes the odds. For example, not everyone with obesity will get diabetes, but it increases the risk. In the same way that not everyone who smokes will get lung cancer, but the risk increases.
Genetics play a big part, as they do at any size. Family history can provide a guide, but no more.
Obesity is not healthy and most of us will probably die earlier than otherwise, but most of us accept that because we like eating and/or getting fatter.
These things cannot be pontificate on in absolute terms:too many unknown variables in terms of genetics and of course what you eat etc has an impact. All that can really be said is that generally, obesity is bad for you.