I often see claims that they are only used to people your own age or younger. But is that true, or an exaggeration based on the fact that you'd use more polite forms to someone older, usually? For example, could you use them speaking to your parents, with whom you'd use the plain form anyway?
They would sound pretty funny talking with your parents. In fact, a lot of Japanese people use ですます form with their parents.
There are a lot of regional dialects in Japan and that could influence their usage (though as you surmise age tends to be the most significant factor), but in this case I think they really are uncommon with younger 関東 people. Maybe なんだい...sometimes. そうかい... Hmm, yes, rare, even these cases is sort of like imitation/acting more than actual self.