You can configure a retention policy that will automatically purge data as it ages.
Also, InfluxDB does a MUCH better job of handling large databases. And in practice I see between 1-6 mb per Item per year which isn't that big of a deal size wise.
And, unlike rrd4j, InfluxDB had a nice way to interact and delete data as needed through it's rest API.
And records can be deleted through OH's rest API also.
Setting up a retention policy and a discussion of database sizes are included in the tutorial link Christoph provided.