I'd say anything less than 70% on the Age Graded Calculator, which would put a runner below Regional scale and into the "Athlete" category.
From their website, it defines each category by percent:
"Age Grading: how it works
Age grading uses tables of "age factors" and "age standards" to put all runners,
regardless of age and sex on a level playing field. In particular, they allow
runners' performances, no matter what their age, to be corrected to what they
would have been achieving in their prime years, and permit valid comparisons to
be made between people of different ages.
>100% = World record level
> 90% = World class
> 80% = National class
> 70% = Regional class"
In case you aren't familiar with it, there is an online calculator where you can plug in your times for any distance to get the percentage rating for your age/sex. It's called "Master's Athletics, Age Graded Calculator"