I always think of teenager as the formative years that influence the adult. So when I hear such and such a time kid I think its refering to that time even though its sorta just past the kid years. I feel like when your a kid your just sorta a kid and not as plugged into whats going around timeline wise and then like preteen you are sorta getting an idea but mostly just imitating or hero worshiping. Teen seems like when really started deciding what they liked and did not like. so rebellion and obsessions and such. Granted people change a lot from that time to but to me it feels the most about when a time periods. I dunno. Lets say flavor really sets in.