EM12C can display historical metrics for up to 31 days (eg CPU/memory/disk/filesystem usage)
Is it possible to keep say up to 1 year of such data?
Yes, that can be done. See the manual: Maintaining and Troubleshooting the Management Repository
But: it will cost you a lot more disk space and probably performance viewing this higher detail level.
But II: I do not know of a way of keeping just the history for metrics like cpu/memory/disk/fs usage.
Or check MOS note: How to Modify the Default Retention and Purging Policies for Metric Data? [ID 1405036.1]