Kinda bummed at the lack of comments yesterday. I was hoping this'd generate a bit more discussion. Anyway, here's part three.
CHARACTER AGE, AGING, DISEASE, AND DEATH
Character Age: Pretty standard fare for games of the 70's and 80's; tables for determining starting age for player characters, followed by age ranges for human and demihuman species (including subraces of elves and dwarves--this is somewhat intriguing since these subraces won't show up as PC types till Unearthed Arcana). Following the age category table, we see ability score modifications based on age. Again, the typical; as you get older you get weaker but wiser and more intelligent...which is amusing considering that we now know that IQ actually drops as we age, but I guess it represents experience and education.
Next we have the number of years added to a character's life for the casting of certain spells or imbibing of certain potions. Useful stuff...again, for players. Should've been in the PHB.
Disease: This section is, IMO, one of the most fun sections in the book. It's got a great rundown of how diseases of various types of infection, including virii, bacteria, and parasites, can be contracted and how they affect player characters.
It occurs to me as I'm reading here that there are not, as is popularly believed, a ton of different systems for handling all different situations in AD&D. There are two: there is a system based on rolling a die and attempting to hit a target number, as seen in combat, surprise, detection of secret doors, etc., and there is the percentile system. Every element in AD&D is handled via one of these two methods. We'll deal with the reason surprise is, at its core, handled with a d6 rather than a d20 later on, but the core resolution mechanic remains the same; roll a die and check the result against a probability, or roll percentile dice under a modified score.
In this case, disease infection is handled based on a percentile score, modified by such factors as whether the character is already infected with an ailment, what the environment and weather conditions are like, the character's age, etc. These factors are added to the base chance of infection and percentile dice rolled; if the result is under the modified chance of infection, the character contracts an ailment.
If the character contracts an ailment, another chart is consulted, from which the DM can choose an appropriate illness or roll randomly. Instead of a laundry list of real-world diseases and parasites, the chart lists infection types, such as blood, bone, brain, gastro-intestinal, etc. It's actually a fairly elegant way of dealing with the problem of the countless varieties of infection in the world.
Again, overall this is one of my favorite parts of the book, though I'm not sure how often it'll actually come into play. Still, it's quite comprehensive and very well thought-out. Where Gygax sometimes seems big on letting the DM wing it for himself, figuring things out as he goes along (such as with the Secondary Skills mentioned earlier), other times he loves to be quite detailed and comprehensive. It's uneven, but somehow charming in its quirkiness.