I'm currently playing Might and Magic Book One and I was wondering if the age of your characters actually functions as a kind of timer or whether there is a way to make your characters younger at any point in the game. Any help would be appreciated.
In MM1, characters age one year whenever they level up (which leads to odd situations where some characters age faster than others). Also, some enemies can age your characters, and casting certain high-level spells will age the caster. Very old characters receive a penalty to stats (I think) and can die when resting. Fortunately, the Rejuvenation spell will lower your characaters' age, and there are other ways to lower age as well.
Practically, you only have to worry about age if you're casting lots of spells that age the caster or if you're facing lots of enemies that can age your characters. Casting Rejuvenate repeatedly can usually fix any age problems you have.
In later games, time is actually modeled, and months and years will pass as you play. Characters age normally over time but can also be artificially aged by certain enemies or events. Later games make a distinction between "natural" and "artifical" aging, and there are ways to remove artificial aging. Again, it's rarely a problem since artificial aging can be reversed without too much trouble.
EDIT: Just to be clear, character age does NOT act as a time limit on the game for any of the games in the series. You have as long as you need to complete the games.