Crick suggested that RNA was the original encoding for genetic information, then it was replaced by DNA.

DNA is more stable and reproduces more accurately.  This explains the strangely indirect protein synthesis using both DNA and RNA.

Viruses use RNA only.

Is there any species of virus that does not need a host?  In other words, in there any remnant around of free-standing life using the archaic scheme?

How old are the DNA molecules in my body assuming I am 65 years old?  How old are the DNA molecules in an amoeba?