At the same time it is not very good "" normal "", that a child of 12 years is interested in the sex and the sexual relation.
Or even talk about sex with a child of 10-12 years, he knows the difference between a man or a woman yes but that's it.
In my case, I learned all alone what is sexual, it is not my parents who spoke to me about it.
Until I was 15-16 girls did not interest me more than that, not that I was not attracted but here it is.
So I understand the situation of natsu well.
By cons Natsu is lucky to have lucy, I would have liked to have a girl in love like that at the time or even today T-T.
Goku ended up getting married, yes, but he did not know what marriage was, he kept his promise to fuss, because he promised, but does he really like "" the question again today.
Besides, chichi went from the girl in love, to the authoritarian woman with him XD.
With DBS, we learn that he never kissed fuss, that he was not there, at the birth of gohan.
Soon we will learn that he never made love with chichi XD, she told him to land on the bed and it is she who did all XD or she did that while sleeping XD.