D&D 3.5 rules specify the effects of aging when reaching middle, old, and venerable age. These effects are the same for all races, with only the age at which they’re reached changing. Forgotten Realms lore states that elves age gracefully and remain full of life until near death. So why should they get the same penalties of age that humans get? Has this ever been addressed?
It reflects lore already established in AD&D 2nd edition.
PHBR8 The Complete Book of Elves (1992), p. 37-39, describes that elves "do not feel the effects of age as humans know them". However, this mainly describes their appearance. It notes that they still suffer aging effects when they reach middle age. Page 38:
At the age of 175, elves reach middle age. They have slowed somewhat and become slightly more vulnerable to disease and age.
And page 39, Old Age:
Around the age of 250, the elf has entered "old age". He still hasn't become visibly old, but he feels the effects of age. [...]
The mechanical stat adjustments show that elves lose Str/Con and gain Int/Wis at middle age, which for high elves begins at 175 years. Similar mechanical adjustments occur at Old Age (250 years) and venerable age (350).
The original 3.0 Player's Handbook (2000) likewise has a very similar aging pattern for elves: they reach middle age at 175, old at 263, and venerable at 350. The Player's Handbook is thus simply reflecting earlier lore established in The Complete Book of Elves.
The AD&D 2e Player's Handbook (1989), p.24, presents similar a aging pattern for elves (at 175, 233, and 350 years). A similar pattern of elven aging even appears in the AD&D 1e Dungeon Masters Guide p.13, except that elves are much longer lived, but still suffer aging effects at middle, old, and venerable age.