Thirty is a joke, seventy is a tribute, and the two in between depend entirely on the person.
Choose a funny card when the person makes jokes about their own age, and a warm one when they do not. That single test is more reliable than any rule about which decade gets which treatment.
Thirty is the milestone people are least sensitive about and most likely to celebrate loudly. Vintage-year designs work well here because the year on the card is recent enough to feel like a badge rather than a reminder.
Forty is where the two camps separate hardest. Half the people you know will want the number mocked, and the other half will notice that you mocked it. If you are not close enough to know, go warm.

By fifty most people have made peace with it, and the mood shifts back toward celebration. Vintage-year and "aged to perfection" designs work because they treat the decades as accumulation rather than loss.

At seventy and above, jokes about age stop being a shared laugh and start being a comment. Elegant, floral and typographic designs carry these better, and the message inside matters more than at any other milestone — this is a card that gets kept.
Editor's pickTwo to four business days in production plus three to seven in transit for US delivery. For a dated birthday, two weeks ahead is comfortable; one week is tight but usually fine.
$19.99