Maybe I need to give more context...
Ignoring the crazy stats snowball effect, in the new player vs veteran the veteran will most of the time go on top in the mirror match (same creatures and tokens) since darkshield is not capped, 4000 defense is better than 300 defense with all the multipliers for example. Adding more features that rely on age will just give another layer of why "your creatures will never be as good as the old ones".
If artificially increasing age is not wanted, how about capping age effects?