Hi,
Since you are using the INFINITY datasource and your data is already in JSON format then I suggest you just use the JSON option as is.
As you do not have many levels of nested data just use the Columns selector to select whatever JSON data you require as shown below
Now as you can see key_as_string is in string format and you want to transform into datetime to be able to use the Timeseries chart panel.
One may then use the Transform data option Convert field type as shown below to convert from string to time.
And it is done. Select Times Series as the visualization option and you get
I have added this as although UQL is indeed very powerful it takes a lot of getting used to and sweat if you are not a dedicated programmer.
What many do not realise is that one may traverse the nested levels using the . operator.
In your case all data bar the value is not nested.
One may access it using average_of_age.value
Also when using UQL if time data is not correctly formatted then using the Time Series Chart it will throw errors until time is correctly formatted so it is best to start with using a Table Panel.
Anyway hope this helps a little