Hi @Odil! There's currently only limited support for filtering OData, particularly for filtering subtables.
In general, we don't plan to support filtering on form fields (like age) in the near future. See this forum post for some of the reasoning behind that. However, we support filtering the primary table on specific metadata fields.
We would like to add the ability to filter subtables on those metadata fields. We have a GitHub issue for that feature here, and there was related discussion in this forum topic. With that feature in place, you would be able to filter a subtable on __system/submissionDate. However, we aren't sure yet what the right approach or syntax within OData would be for that.
It is currently possible to fetch a subtable for a single Submission:
/v1/projects/{{projectId}}/forms/{{xmlFormId}}.svc/Submissions('{{instanceId}}')/{{repeatName}}
(Note that xmlFormId and instanceId should be percent-encoded.) However, that doesn't provide a way to fetch data for multiple Submissions at once.
Hope that helps!