The birthday poem that is not about birthdays
Christina Rossetti's “A Birthday” sounds like a birthday poem, and it is a love poem. Its speaker's heart is “like a singing bird” because “the birthday of my life / Is come, my love is come to me”: the day that counts is the day love arrived. It is a lovely line for a partner, an anniversary or a wedding, and an odd one for a nephew turning nine.
Mark Twain and birthdays
Twain is the name most often printed under birthday jokes, and most of those jokes are not his. “Age is an issue of mind over matter. If you don't mind, it doesn't matter” is not found in his writing; the earliest version Quote Investigator located is from 1968. The line in this room, about wrinkles and smiles, is in Following the Equator, so it can carry his name.
What is a good short birthday quote?
Shakespeare's “There was a star danced, and under that was I born” (Much Ado About Nothing) and Twain's “Wrinkles should merely indicate where smiles have been” (Following the Equator) are both short, and both traced.
Did Mark Twain say “Age is an issue of mind over matter”?
Not as far as the record shows. Quote Investigator's earliest version is from 1968, credited to an anonymous government researcher, decades after Twain died.
Where does “un-birthday” come from?
Lewis Carroll coined it in Through the Looking-Glass (1871), chapter VI, where Humpty Dumpty explains un-birthday presents to Alice.