@Tatherwood not that I care about the issue as a whole but "old enough to masturbate" isn't really a good argument against @leusee argument, That's like a terrible barometer.
@ziggy7570 It is, considering the original argument.
If it was "he's a minor, it's illegal" there would be a different counterargument.
But the "argument" (I have trouble calling it that) was "he's a kid".
First, he's 14-15, hardly a "kid".
Second, BECAUSE he's 14-15, he's sexually mature, interested in girls, in sex, and old enough to date. Just not old enough to date someone older than 18 (legally).
Third, he likes her (and he's old enough to understand those feelings, generally).
Worry not he is getting legal soon. It's male and female relationship. It's not that dangerous. I think the onee-san understand it well. It's normal for a woman to fallen for younger boys. She will act accordingly.
@Xxjuggernaut
Between prepubescence (kid/child) and adulthood there's something called pubescence (teenager).
You may or may not have heard of it. Experienced it, even.