Can I join National Pension Plan (Kokumin Nenkin) even if I am over 60?

You may be able to do it.
Those who are Address in Japan and who are between 60 and 65 years old or Japanese who have Address overseas who are under the age of 65 are eligible to join National Pension Plan (Kokumin Nenkin) at their own request.
As a general rule, the registration procedure is at the ward office National Pension Plan Section in your ward.
However, please note that if you pay National Pension Plan (Kokumin Nenkin) premiums for 40 years (480 months), the amount of basic retirement pensions received from the age of 65 will be full and cannot be paid further.

・My number card or pension notebook (basic pension number notice), etc.
・Notification stamp of financial institution
・Financial institution bankbook

Insurance and Pension Division National Pension Plan Section, each ward office