Quick Question About User CP

Is there a limit as to how many subscriptions you can store in your folders (in GB)?

If the limit is in gb, then you’ll likely never need to worry about it.
I doubt there is a limit, however.

I was just wanting to know if I should delete subscriptions that are a year old or older. I would prefer not to, so as to avoid repeating threads.

In all likelyhood, topics over a year old will already have replacement topics.
I think you’re safe to remove them from your subscription list, if you feel the need. Alternatively, you could bookmark all the pages you feel important, and check up on them whenever you feel the need.