Old is time tested and trusted and hence it is called as gold. New is fresh and yet to be tested; it may or may not give the desired result and hence trusted by "few"
old is gold because, the old things arent made anymore, and hence, they are almost rare, almost like gold. The old things are worth a lot too, like gold. Thats why old is gold.
Old is full of experience,can take the right decision in right moment.New yet to have face the situations those already faced by Old.