I think if you investigate the speculations of those in the 17th century you
will find they were motivated by a consideration of scientific data, not
biblical data. As for Origen and Augustine, they doubted that Gen 1 needed
to be understood as literal history; and that is an important point. But,
there is no evidence that they or any other early Church father doubted that
the universe was older than 6000 years. Taken in a straight forward way the
biblical genealogies infer a very young universe; and that is the way the
Church as a whole understood them until scientific data demanded a
reinterpretation.
Even if Origen doubted that the days of Genesis before day four were literal
24-hour days (and I would like to see the reference in his works before I
admitted even that), he could just as well have been thinking they were
shorter than 24 hours as longer. Augustine (and I believe a few other
fathers) questioned the literality of the creation week because Gen 2:4 spoke
of the heavens and earth "in the day in which they were made." He reasoned
from this that the creation could have been done in one day or perhaps less.
Unless there is concrete evidence to the contrary, the probability is that
Origen agreed with the rest of the Church that the universe was not older
than 6000 years.
The idea of a universe older than c. six or ten thousand years does not arise
naturally from Scripture. It has to be read in from science.
Paul