The same topic was previously covered:
http://www.japanforum.com/forum/livi...e-society.html
You Simply have to throw your believes away, understand and adapt to how the local people will react. This is not something that "carried over" from old age only.
Some argue that rock star and celebrities have tatoo as well, however, chances of them going to a public bath is skim, and if they do go to an onsen, their agency will probably make prior arrangement