account items association

No idea what "deactivate old items" means.

Please explain

I assume you mean the number of authorized computers and other devices associated with your Apple ID. To see this info (iTunes 12.2) select Account > View Account and enter your Apple ID and password. The next page will include info like this:

1. Total number of computers authorized to play/sync media purchased using your Apple ID from the iTunes Store. You can deauthorize a computer within iTunes by selecting Account > Deauthorize This Computer ... - your computer can no longer play or sync any media purchased from the iTunes Store.
2. You cannot deauthorize a computer that you don't have access to. You can, however, use the Deauthorize All button to reset the number of authorized computers to zero (this is the only info that Apple have) and then reauthorize those that you have access to. Note that you can only use the Deauthorize All function once every 12 months.
3. This is the number of computers and iOS devices (iPhone, iPad, or iPod Touch) that have been associated with your Apple ID and can access purchased items from the cloud. Note that this may be somewhat different if you're using any combination of iTunes Match, Apple Music, and iCloud Music Library.
4. Click here to see details of your cloud-authorized devices.

In earlier versions of iTunes these features are accessed via the Store menu.