Let's say that life expectancy is now increasing at a rate of 2 years per decade. If you want to live to 1000, you just need to increase that to 10 years per decade. You don't have to go from 78 to 1000 all at once.
Personally, I expect false starts in the next couple centuries. The beta testers will be healthy and fit into their hundreds, but those that follow may get to 200-400, then possibly further. There are just too many engineering issues to work out in a single iteration.