Depends. If it's a form I'm filling out, I'll either put the real one or not put one at all. If I'm just being asked "enter birth date to continue", not really. I mean I sometimes do, mostly out of habit, but generally I don't bother. I passed such questions before I was 13/14/18/21 as they're completely useless in just about every single way (apart from making you lawsuit immune I suppose) and I still do now that I've past all those ages. Just click the first long-ago year you can come across, the point of the question is whether I'm older than a certain age, not when I was born.