this age is called Golden age because the metal gold is widely used in this age by average men in majority of household goods and appliances. 

Treta (The Third) 
This is the third age or the mental age. This age is characterized by a fall in spiritual consciousness. The Bull of Dharma has three legs. Moral and ethical values decline a bit. Although much spiritual awareness is lost but mental awareness remains very high. This is the age of the mind and the development of mental faculties. Time is conquered in this age. Human beings can frequently go back and forward in time that is know their past or future quite easily. Average mental powers like mind healing, thought reading, mind travel etc are performed effortlessly by many people though not everybody. In Greek mythology this age is called Silver because in this age the metal silver is widely used and not gold. 

Dwapara (The Second) 
This is the second or the space age. In this age man conquers space. Space travel through fast atomic vehicles and interstellar travel becomes possible. The subtle forces and energies in the universe becomes known and man uses them for his comfort. Moral and ethical values decline further. The Bull of Dharma has two legs. Man comprehends the subtle energies in his body and in the universe. Much awareness exits about the energy body of man, the aura. Aura healing, cleansing, detecting sicknesses in the aura etc. becomes very common. Bronze and copper becomes the most widely used metals. 

Kali (The first) 
This is the first or the age of matter. This age is characterized by total loss of spiritual awareness and mental faculties and average man comprehends only his gross physical body and the gross matter that he perceives in his immediate environment. Moral and ethical values are at its lowest. The Bull of Dharma has only one leg. Widely used metal is iron. The historic dates corresponding to the yugas as calculated and given by Sri Yukteshwarji in his book, 践oly Science' written in 1894 when modern astronomy did not have the big telescopes or the wisdom they have today: 

Descending Half  

Ascending Half  

The world is presently in the ascending Dwapara Yuga and entered this Yuga around 1699 A.D. We are therefore three hundred years into this higher age and this age will continue another 2000 years or so.