One funny birthday card message is, "You?re old enough now that running your mouth is easier than running yourself anywhere." Another funny message is, "Doctors suggest staying out of the sun to avoid premature aging. You must have lived in a cave your entire life."
There are many funny messages to write inside birthday cards that emphasize how old a person is getting, particularly messages such as, "To the nation's best kept secret; your true age." Another funny message related to age is, "Better to be over the hill than buried under it." There are also many lighthearted sayings that do not relate specifically to age, including: "Just imagine the things you?d want to hear on your birthday, and assume I said them. Happy Birthday!"