True, you have the freedom to play down holidays and birthdays, and many older people in fact do (who wants to be reminded that they are getting old when they hit 50 and 60?). However, you might wish to take a good look at the reasons for keeping your old beliefs from the witlesses.
To start, if you are not celebrating Christmas or birthdays for religious reasons, I suggest looking at Luke 2:10-14 objectively. There, it speaks of perfect angels celebrating Jesus' birthday without getting in trouble for doing so. That will help you realize that it isn't wrong to celebrate a birthday or Christmas if you so feel like it.
Obviously, there may be personal reasons for not celebrating certain holidays. If you are single with no prospects, it might be hard to get into the spirit for Valentines Day, regardless of its origin (and that is a valid personal reason to choose not to celebrate it). There may be other personal reasons to forgo or limit a holiday--money among them.
Each belief you keep or shed has an opportunity cost and benefit. Some beliefs can hold you back from making friends with the world. For instance, even if you keep Christmas low-key yourself, a Bah! Humbug! attitude will in all likelihood make them think you are still a witless. A better approach might be to accept their celebrating and go along with it to a degree. A simple "Merry Christmas" or "Happy birthday" can make the difference between being accepted and being pegged as still a witless. You alone will have to decide if a belief is holding you back, and if so, is it worth discarding. I might add, however, before you ditch beliefs, you should research them so you can find the appropriate truth (and research from several independent sources) and not return to an erroneous position.