Also,Japan has the age of consent at 13,many prefectures bump that up to 16 at least,and teens getting laid is common in all nations,so...
The law is not the same as morality. And yeah, teenagers have sex with other teenagers. That's obviously fine, and not relevant to this.
Teens get laid in every nation,and it can be with other teens,some are bad enough to do it with younger,and plenty do it with older.
More so when cold hard cash is involved and/or the general regions' living conditions are tad bit low.
The laws are what they are,but morality is meaningless when feelings are involved,and boy oh boy,did those feeiings explode.
Also,pedophilia is for those who target 13 and under,depending on puberty,and usually pre-puberty.
Hebephilia is for those who target 11 to 14 or slightly above,usually in the midst of puberty.
And what we see here is ephebophilia,15 to 19,the late puberty stages(all three have overlaps with each other becauase RAGING HORMONES).
But,as in this case and many one on one couple romances,the older one is mainly,if not exclusively,attracted to their partner,who just happens to be younger.