Why do transactions with lower input age require higher fees? I am trying to understand how bitcoin fees work. I have understood well why transaction with many inputs require higher fees but I can't figure out why transaction spending virgin bitcoins would require important fees as well.

The logic behind my thinking is the following:
If my inputs are a recent coinbase transaction, it is easier for the nodes to check their validity as they don't have to crawl the whole blockchain up. So it should require less time/processing power to validate them, which would mean lower fees.

Apparently there is something wrong in here :) 

Does anybody have a better explanation?
There is no time difference to check old or new outputs, because the database of them (UTXO) is a HashTable. The reason to take obligatory fees from new funds is preventing useless transfers from one account to another wasting the blockchain and increasing its size without reasons.