From the very moment of creation, mankind was predestined to eternal life. Having been made in God's image, God, in His infinite wisdom gave us free-will; not to believe in Him because Adam and Eve new God as their Father, and God knew them as His children. This free will, like that of the fallen angels is one way, we can only chose to defy God.
This has not changed. God is our Father, we are His children; we have no choice in this. God is the perfect parent, He wishes only the best for his children (all of mankind); salvation and eternal life. We, however, just like earthly children with earthly parents, we can chose to defy our heavenly Father the way some children chose to defy and estrange themselves from there parents.
This is exactly what our Lord illustrated for us in the parable of the prodigal son. The son squandered his inheritance and became estranged from his Father, just as we can turn away from God (by our choice) and lose our salvation. While he was hopeless and knew he deserved nothing more from from his father, the father still loved his son and restored his position.
This shows us that we only have free-will to reject, not to accept God; this also shows us that we can fall from grace and lose our salvation, yet repent and have it restored.
This blows double predestination right out of the water, as it does once saved, always saved.