This is the case when the grammatically correct phrase misinforms. 17 y.o. infant is young enough for not to be considered an old man or even a grown-up (he is legally underage), but he is not a target of the kids-proof packages.
Technically or not technically, nobody would apply the term "young child" to 17 y.o. It is not about having kids of your own, it is about the usage of the words in live language. 20 years old is already a "young adult". And saying that somebody N years "old" does not mean that he or she is really old.
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