One way is to use PQL where you can compare the contract date and today's date (Profile Query Language)Another not-so-great way to put this is (Read Birth Date as  Contract Date): 

You can start by looking for the profile_snapshot_export_<mergepolicyid> dataset after enabling the Show system dataset in UI. (based on the merge-policy available, you can see multiple entries). And below basic query should give you result for the segment membership SELECT to_json(identityMap),...

Yes, it will just link the 2 emails, which I don't think will be an issue as they are the same email but just different hashing.

If you can provide more details/context, Merge Policy can be evaluated as one of the options.Generally speaking, Profile attribute history is not supported in segment builder unless the data is captured via timeseries modelYou can also look for the profile snapshot table, where you can copy the whol...

You can use data prep to calculate age but the this will not be recalculated unless you ingest the record again.I would either, based on requirement, use Query Service or just create segments to qualify users in certain age groups