Oldest population 1 star system?

You would be very interested in one of the recent Kepler discoveries - Kepler 444. The star is estimated to be 11.2 billion years old (using asteroseismology) and is surrounded by a number of rocky exoplanets. These planets are all too close to their parent K-dwarf star to be in the habitable zone, but there is no reason there couldn't be planets further out. The star has a metallicity [Fe/H]=-0.55 (i.e. about 30% if the Sun) and is part of the "thick disk" - i.e. somewhere in between populations I and II. This demonstrates that rocky planets can have been around at least this long in our Galaxy - which is I guess the main point of your question.

As there is no clear dividing line between population I and II (it is a combination of kinematics and metallicity that can be used to make some arbitrary dividing line) then no definitive answer to your original question is possible.

The enrichment of the Galaxy by metals takes place very quickly in some places (e.g. the Galactic bulge - probably in a billion years or so), but in more leisurely fashion in others (a few billion years), and then plateaus. Stars born today are not more noticeably metal-rich than the Sun on average. The other problem you have is that stars probably don't stay put and migrate to different radii.