Moses asked how many fat 90 year olds are around.

I have no data to offer, only a thought, that the frail 90 y-olds may in at least some cases have been very robust 70 y-olds.

When young I had a number of large elderly female relatives (the males mostly seem to have been on the small side, and short-lived) some would have been obese by today's standards. My paternal Grandmother, for instance had a 54inch bosom, a behind to match, and was around 5ft3in tall. Most of these ladies lived well past 80, some into mid-90's. By the time they died they had mostly shrunk again, ending life not exactly slender, but certainly not their former selves.

While it is not generally a good idea to carry too much weight, it should not be seen as an automatic recipe for a short life.