Some types of early onset (EOA) are, there is no good evidence that other
types are. bear in mind that at age 85 over 50% of Western population has
it, so if you have a fair number of elderly relatives, you'd expect quite a
lot of them to have it just by chance.

Lets face it, aside from EOA, if 50% over the age of 85 have it, you really
dont need to worry about whether its inherited or not, because if it is ,
its only going to add  a very tiny percentage to your chances of getting it
(because if it was more than tiny it would have been discovered by now).

Chances are its a combination of genes, diet, lifestyle and maybe just luck.
And you'd go mad (!!) if you tried every combination of diet and lifestyle
recommended to reduce your chances of getting it! Though Diabetes does seem
to show as a risk factor according to some recent studies, so having a diet
that is good for not getting diabetes probably wont hurt.