How old should be my bitcoins to send them again without transaction fee? I'm making some test for a bitcoin merchant webpage. I want to test different actions without paying transaction fees everytime, but I can't since I use the same few bitcoins for everything.

Sooo how long should I wait for my bitcoins to be transfered wihout fee?
As the coins "age" they will have a higher priority.

I don't know the algorithm, but believe it is roughly like a day or so and then the age of the coin no longer is a factor.

So if you are seeing minimum fees for coins more than a day after you've received them, it is because of other reasons, such as having outputs at amounts below 0.01 BTC.