You don't have to, but it will help avoid a lot of snark as well as well-intentioned but annoying jokes (like the babel dev described), not to mention less visible discrimination like being passed over for promotions, being given worse projects and so on.

There are also programmers whose pride is damaged by doing the same work as someone much younger than themselves.

Remember (at least in the US) age is a protected category and you can't be asked about it during an interview, so if you're careful about how you write your resume no one really has to know exactly how old you are.

Good luck.