Beta Upgrade 
theres a story about this very idea already 'forever young' or something i think its callled
flutershy discovers at some point discord is preventing her from ageing
||she tells him to stop, agreeing to it only if he can convice all her freinds to accept the same...he fails, and unwilling to accept a world without fluttershy, he revokes his own immortality with his magic allowing his body to begin to age...a year after fluttershy passes away, having seen to her earthly affairs for her and assured that her sanctuary was taken care of by another who was worthy, he passed on as well to rejoin her in the great unknown||
flutershy discovers at some point discord is preventing her from ageing
||she tells him to stop, agreeing to it only if he can convice all her freinds to accept the same...he fails, and unwilling to accept a world without fluttershy, he revokes his own immortality with his magic allowing his body to begin to age...a year after fluttershy passes away, having seen to her earthly affairs for her and assured that her sanctuary was taken care of by another who was worthy, he passed on as well to rejoin her in the great unknown||