Even before they can talk, they know how many fingers represent their current and upcoming age. Even the shy ones let you know how many years old they are about to be.
Knowing this may be their only chance to have total artistic control, some moms plan the first birthday cake months in advance. We do lots of "over the top" first birthday cakes, with lots of ribbons and bows and stars and streamers.
We almost always do an additional "baby cake" or "smash" cake for a one-year-old's birthday. It's often a smaller version of the main cake.
Six is another big birthday. Not sure why it's better than five, but we do more big birthday cakes for six-year-olds than five or seven.
Then it's the first teen birthday at 13. Currently it's tie-dye and peace signs and zebra prints. Some kids band together to celebrate a group of birthdays. This way the kids can have a big party and big cake, and two or three moms can share the expense.
Then Sweet 16. Often the first big "grown up" party cake. More sophisticated than 13, but still fun. Lots of pink and black here, with lacy or bold designs. No more licensed characters or peace signs.
Then 21. Martini glasses are the single most common design on a 21st birthday cake, and usually bought by mom and dad or a boyfriend or sorority sister. University of Alabama (Roll Tide!) is also popular, after all, this IS Tuscaloosa!
My birthday is coming up later this month, how old will I be? Well, let's just say that when you get to an *ahem* certain age, you no longer want a number on your cake.