This is a difficult question to answer.

Mostly because everything you wrote as reasons, i would throw out as beyond shtupid, but there are a lot of things you aren't seeing that will make 100 years old seem like nothing.

While much of that could be a bit far-fetched, there is no doubt that progress is being made. Research such as the mapping out of the genome as well as DNA editing could help to alleviate many diseases such as cancer, dementia, and strokes.

This as an example.

DNA has nothing to do with these things.
Editing DNA will not fix any of these things.

But the really hard part is that, fixing these things will change your DNA. (if we were able to read DNA that accurately)

Currently we are treating cancer with radiation.
Really! Does a body develop cancer because of a lack of radiation? A radiation deficiency?
No.

Cancer is actually better cured through diet.
But we are sooo shtupid about diet, that we still measure food in calories.
We haven't even begun to look into what is nutritious in food.
There are a few people working on calibrating nutrition numbers.

As an example, would you eat at McDs if you knew it has 0 nutrition?
It would make it so much easier.
McDs -- 0
Tomato, green ripened with kerosene -- 100
Oraganic, vine ripened tomato -- 500

We currently work with 1/7th of the body.
Allopathic medicine (rots-child medicine) will be seen as being more idiotic than using leaches appears to us.

We will see all kinds of advancements that seem insane.
Like tinctures (chemical amounts so small that they can't be measured but have an effect on the body)

So, the future is bright for living a lot longer.
700 is closer to the actual normal age a body is designed to work before it breaks down.

However, the coming ice age, economic collapse, floods, freezing and fires will be difficult on lots of people.
Those that survive will probably see 2100.