InfluxDB

Is it possible to add a retention policy?

You can select and update the duration (how long database keeps the data). This feature is available only for higher pricing programs (different than “Free”). Shard duration is set to one week and it is not possible to change it. Please, do not hesitate to contact us if it is blocking for you.

You act like Non-admin user so you could not add a retention policy directly.

Is it possible to delete points older than a given time manually?

Yes. For more info see DELETE command.

Example:

delete from "meas_test" where time < now()-2d
delete from "meas_test" where time < '2016-01-01'