Phylactery of long Years: This device slows the aging process by onequarter
for as long as the cleric wears it. The reduction applies even to
magical aging. Thus, if a cleric dons the phylactery at age 20, he or she will
age 9 months every 12; so that in 12 chronological years, he or she will
have aged but 9 and will physically be 29 rather than 32.

1 in 20 of these devices are cursed to operate in reverse.