The advent of cloning allows scientists to create genetically identical embryos that age normally. Unless a clone is created during the first year or two of a person's life, such a significant age difference exists between the original person and the clone that they are more akin to parent and offspring than to identical siblings. The next quantum leap in cloning technology comes when scientists develop the ability to artificially age the clone. Rather than wait for the embryo to age normally, this advance allows the clone to mature at an accelerated rate until it is an exact replica of the donor (minus scars, tattoos, and other acquired physical modifications).
Artificial aging is an important part of clone fiction, but it is such a hypothetical process that it is difficult to place it at a particular Progress Level. Perhaps this ability would be linked to developments in battling the aging process. Or there might be a relatively simple way to stimulate embryonic clone cells so they continue to grow at the same advanced rate even after the fetus becomes a viable infant. This allows the clone to grow to full maturity in a matter of weeks or perhaps even days.
In a setting where the GM wishes to be as scientifically realistic as possible, artificial aging is not developed until PL 9. However, in campaigns where individuals are able to have a cadre of clones to serve as organ donors, replacement bodies, and heirs, the GM may rule that artificial aging is developed at PL 6, at the same time that cloning technology overcomes the viability problem.