It's illegal to ask an applicant his or her age. This law was designed primarily to protect people over the age of 40. However, it is legal to ask applicants if they're over 18. If they're not, you need to know because of federal, state and local child labor laws. What's crazy about this law is that you can't ask someone how old he or she is in an interview, but you can ask for date of birth on an employment application. You figure it out!
Excerpted from Attracting & Rewarding Outstanding Employees