Young PCs receive the following adjustments:
- -2 Strength
- The character's size is reduced by 1 category.
- If the character's base speed was 30 feet or faster, it is reduced by 10 feet. If their base speed was 25 feet or less, it is reduced by 5 feet.
This option is intended to represent exceptional, very young children. Prodigies, the results of magical experimentation, or otherwise precocious youths, but not teenagers or people just slightly under the line for adulthood- run those characters as adults, as they're not small enough for their size to make a difference. If we were attempting to be realistic, child characters would likely be crippled beneath playability- these are children along the lines of Harry Potter, Peter Pan, or Ender Wiggin. This is only an option for medium and small creatures at this time. Other adjustments would be necessary for creatures of other sizes, if they were even desirable.
A standard size adjustment as defined by most Polymorph spells and altering monsters in the Bestiary usually carries a +2 bonus to Dexterity when making a Medium creature Small. This functions fine for buff spells that provide a specific benefit and for monster adjustments that are made with sanity checks against similar creatures in the bestiary and often times adjustments to natural armor. In practice, when applied freely to PCs there are a lot of cases where those alterations result in characters that are strictly stronger than their full-size counterparts.
The reduction in size category alone should be a significant enough benefit for being young. You're a smaller target (+1 to AC) have situationally better accuracy (+1 to-hit), and are much better at hiding (+4 to stealth). Conversely, you also have a harder time manhandling others and are easy to push around (-1 CMB and CMD). Combined with a reduction in speed commensurate with smaller sized creatures (for example, see gnomes and halflings compared to humans), you should be roughly as powerful as a normal character. This isn't supposed to make you any more or less powerful, after all.
Instead of the usual rules for aging, refer to the following chart:
Age Benefit Penalty Adult None None Middle Aged Routine Aches and Pains Old Routine, Wise Aches and Pains, Faltering Senses Venerable Routine, Life Well Lived Fragile, Faltering Senses
Routine: One particular skill has been particularly important to your life, and it's been finely honed by half a lifetime of use. You gain a +2 bonus to checks made with one skill of your choice.
Wise: You've collected a large amount of knowledge. You gain a +1 bonus on checks made with all Knowledge skills, Linguistics, and Spellcraft.
Life Well Lived: The eldest in many societies are revered as storytellers and lorekeepers for good reason. You gain a +2 bonus on checks made with all Knowledge skills, Linguistics, and Spellcraft.
Aches and Pains: Your body isn't what it used to be. You suffer a -3 penalty on all Fortitude saves and Constitution checks made to avoid fatigue, exhaustion, or sleep.
Faltering Senses: As you age, your senses have started to dull. You suffer a -3 penalty on Perception checks.
Fragile: Your body is withered and tired, hanging on by a thread. You suffer a -3 penalty on all Fortitude saves and Constitution checks.
A character gains the appropriate benefits and penalties when they reach each age category, non-cumulatively. For instance, an Old character has Routine, Wise, Aches and Pains, and Faltering Senses, while a Venerable character has Routine, Life Well Lived, Fragile, and Faltering Senses.
In addition, characters no longer suddenly drop dead at a specific age. Instead, a venerable character must make a Fortitude saving throw at the end of each year, with a DC equal to 10 + 1/2 the number of years they've aged past Venerable. A natural 20 is not an automatic success on this saving throw. When a creature has failed a number of these saving throws equal to their Constitution modifier they begin to fall ill, dying of old age within the year. Particularly long-lived creatures (any whose die roll for determining maximum age would have averaged 50 or greater) such as elves save against a DC equal to 10 + 1/20 the number of years they've aged past Venerable, and must only make such saving throws every 10 years.
Characters getting older, especially old enough to enter a new age category, is something that happens extremely rarely in D&D and Pathfinder. In most games nobody is going to start out a hale young adventurer and end up dying of old age. As a result, it's never really been considered an important rule, and when Paizo took over the legacy of 3rd edition D&D, they just left the existing rules as-is. This sucks, because the existing rules for aged characters are really bad. They're nonsensical- your sight gets better when you get older in d20!- abuse-able- it's easy to remove the penalties and reap the significant (for casters) rewards of old age- and sloppy- they hand out ability score modifiers for little reason, which can cause serious balance issues. This is an attempt at rules for aging that are more usable (and won't cause any issues even if someone manages to void the penalties).