Those balloons represent her youth floating away into the distance. 
(via reddit)

Vanity tip: don't lie about your age if you've already handed in your W-2. Redditor 2_minutes_in_the_box had a birthday recently, and as far as her public announcements were concerned, it was her 29th. She did not succeed in fooling her coworkers, who very pointedly made this fact clear on her birthday cake. 

While we don't know exactly how she was found out, it should be noted that many offices have someone who keeps track of birthdays. Often, this person is in HR and has seen your resume and your W-2. At the very least, they know when you graduated. If you lie about your age in the workplace, you're basically just banking on this person to humor you. Which obviously didn't happen this time.

Sources: redditor 2_minutes_in_the_box