Further, I think transparent forging can not be touched so that is out of the question.
The idea about taking the "age" of coins into account can be interesting if you mean the age since last transaction.
This would certainly reward new/active users without creating GODS and GIANTS, so if something like that can be achieved I believe this is benificial.
Taking the age of coins is a good idea imo

Also a forging rate ceiling at a given amount of coins would be good also, thus a forging rate a little more efficient until this ceiling, but it's probably too hard to implement.