I suggest you make sure that if your Accuphase bought in Japan breaks the company will fix it here without your having to ship it to Japan.
They say Accuphase never breaks, but it probably does, rarely.
How old is too old is a good question. Certain parts do age. I would not hesitate to buy , say, ten year old Accuphase.
As for newer vs older, I'll let those better familiar with this brand express their opinions.
Another question that you did not ask. Do you want class A lower power Accuphase or Class AB higher powered Accuphase.
And you didn't mention your speakers, source and cabling.
I prefer more sophisticated sound of Accuphase to Luxman's.