I love the concept of this. Loop hero except you have to control the ages of both your hero and your enemies.
you've left a strategy in that's so overpowered i cant help but see it as an oversight: every enemy spawns at age 0. If you react fast enough, you can kill enemy for 1 mana. Doing this, the game becomes really boring. which is a shame honestly.
I'd probably rework this game quite substantially, the age system specifically. For the player, i'd have players be stronger in youth and weaker in old age, but have "player growth" (the amount a player's base stats increase per day) increase in old age.
that way, it becomes a balancing act between being old when out of combat, and young when in combat.