If you look at the number 2045 you will find that it comes from a roadmap of a Russian billionaire. Making roadmaps can be useful because the can guide action. Especially if a billionaire wants to use his funds in a way that keeps him alive.

Two, you can't tell if a longevity breakthrough has occurred any faster than the rate at which humans happen to live.

That's false. The number 2045 comes from a plan to be able to upload humans completely by that point and not be subject to biological concerns anymore.

And three, why all the focus on this century for people who aspire to live a lot longer than normal?

If we don't get things right in this century we won't live in the next. We do have to focus on this century if we want to experience the next.

It doesn't make much sense to ask why questions in cases like this without seeing the context in which people make their statements.