How to properly measure files aging?

[atatarn]

I have a 3rd-party system as part of my infrastructure, and to measure/visualize/monitor its state I'm using custom collectors.
There are two actors within this system: one produces files on hard disk, and another one consumes them (reads and than deletes).

To get the idea of how fast consumer actually works, I'd like to have some metric here: # of files vs. their age. Age here is simply number of seconds since file's mtime.
The usecases are: alerts on average age being too high, total number of files being too high; and some dashboards covering how many files are pending for 1, 5, 10, and more seconds.

Is it possible to have HistogramMetricFamily (or similar?) out of the following data structure [("name1", 7), ("name2", 23), ...]? Here, each tuple consist of file name and age.

Thanks!