When an evil, post-apocalyptic tyrant targets him for his scientific secrets, the last survivor of a 300 year-old life-extension experiment must find a way to keep his knowledge safe.

I really like the premise of this script… but I think this logline is actually worse than your first attempt.

This logline is not focused on the lead character.

When the last survivor of a longevity experiment is targeted by a post-apocalyptic tyrant, he must find a way to keep the knowledge safe or destroy it forever.