Using old serial number from Adobe - is it still valid?

To add to what JJMack said, the serial keys purchased for software with perpetual license are not valid for Creative Cloud apps. Creative Cloud is subscription based and has no use of keys. So if you decide to use the new version of Photoshop, you will have to purchase a subscription.

-Manan

That would have been CS6.  If you Activate CS6 in 2012 It would be registered to you Account at Adobe.com. Goto Adobe.com sign in with your Adobe User ID and password. Manage your account and click on Plans.  The Click My products.  On that Page you should see your Products. Some versions seem to be blank but you should see the 2012 Date on your Photoshop product.  The Platform your licence is for and your serial number. When you install CS6 you will be asked to enter your serial. If yoru CS6 was an Upgrade you will also need your CS5 serial. from 2010.  If you do not enter a serial it will install as a trial version.  CS6 needs its updates be sure to install them after you install CS6.  Your serial is only good for CS6 Windows or Mac.