I bought World of Warcraft in summer of 2007. i activate my account only during the summers and 2 weeks for christmas. it wont let me copy a pre made character to the player test realm. how come?

There could be several reasons for this:

Player Test Realms are not always active because they are only available when a patch is ready for testing. They will be up for a long time on large patches and for a short amount of time on small ones.

There is also some criteria that must be met for certain test realms. An example is that a WoW account must be active prior to the test realm going live.

You can only have 2 copies of your characters on the test realm.

One of those reasons is most likely the situation, but if it isn't you can always view other reasons on the Test Realm FAQ:
http://www.worldofwarcraft.com/info/faq/ptr.html

Good Luck!