Rather than having a sage class, I decided that it would be good to have an option players can take to in essence be a sage. Like my Berserker option.
This sets the bar for being a sage, and also give the character the sages curse. Basically a player can choose to do it but are not forced to, and if they forget about it, the character is not hampered in some way. The curse part is from an early supplement from Judges Guild or The strategic Review, but I can't remember. So here is my Sage option:
If you have a Magic-User with an Int of 15+ the player can opt for his character to be a sage. The character gains the "sagery" power. The sagery power allows a Magic-User to burn the highest level spell memorized for immediately relevant knowledge. Additionally, they gain the ability to cast a curse when they are close to death or dying because of assault, mayhem or murder as per the curse spell.
Here is a handy curse chart provided by (stolen from) Dyson Logos (cause its dang relevant):
(edited to take out the chart which is linked to - it made things too long and this is not its home)