Thanks for your kindly explanations!

There's something I don't understand however, let's assume that a bitcoin address makes a valid transaction that spend all of this balance, while checking the validity of that transaction you have to go back in time, in transactions and in blocks.

I know now that the antiquity of particular coins can't be determined (thanks!), but antiquity of an address is just how much blocks you had to analyze to tell that the transaction is ok. Isn't?