Well, 16 according to sources (which I think is the average AoC in most of the civilised world) so not really a young child. I think this case is probably more damaging. However the media is very sensationalist about this kind of thing, I think it's a good idea to wait and see before passing too harsh judgement. The statements refer to "nudity" and "naked girls" which for all we know could be pictures from nudist camps rather than actual child porn. If he's actually assaulted any children then yeah, that's terrible and he should have the book thrown at him, but I don't think it's been suggested yet that he has, or even that he's viewed that happening.I think the author of Toriko got prison once for actually paying for a young child for the night, and his manga while put on hiatus did resume after he was out. I doubt this will affect Kenshin much.
He is bound by the rules of the country he lives in. Underage Porn wasn't banned till 2014People in porn have to be 18+ under that age is illegal in most countries.
Actually child porn was banned in Japan in 1999, which is quite shocking as most countries had banned it by the 1970's. Bizarrely possession of child pornography wasn't banned in Japan until 2014 (which is the law you're referring to), however the law wasn't enacted until the following year apparently so people in possession of material could get rid of it. That just astounds me.