It's probably different for each person; "identifying as" is a subjective, self-reported marker. That said, I'm sure at one point you tried out being "punk" or "preppy" or whatever label you were attracted to as a kid. At some point it just sort of... stopped being you. Did all of the factors that made you feel like you belonged to that group disappear? No, some were useful in your general personality. But you stopped calling yourself "punk".