At middle age, -1 to Str/Dex/Con; +1 to Int/Wis/Cha.
At old age, -2 to Str/Dex/Con; +1 to Int/Wis/Cha.
At venerable age, -3 to Str/Dex/Con; +1 to Int/Wis/Cha.
SOURCE: The D20 System Reference Document
After all, characters are not like normal people. They heal quickly with magic, survive things that would kill most people, they come back from the dead (preferably via a Cleric and not a Necromancer) and they are generally larger than life.