Were men born again in the Old Testament?

Yes, without regeneration no man has a nature compatible with God or able to do anything pleasing to God. Without being born again, a man cannot see or enter the kingdom of heaven, or even hear with understanding the teaching of Jesus (John 3:3,5; 8:43,47). Prior to being quickened into life, every man is a willing follower of the world and the devil (Eph 2:1-3). Isaac was born again just like the Gentiles believers in the churches of Galatia (Gal 4:28-29).