does your fiance currently have any valid U.S. visa(s) ?
given that his retirement is near, you are potentially facing an issue in terms of financial support.
as part of a Green Card application based on marriage, the sponsoring U.S. relative and Beneficiary
need to provide adequate minimum income, based on the number of people living in the household.
If your fiance has a U.S. visa, he could enter the U.S. and at a later point, while in the U.S.,
get married, and you could then file a petition for his Green Card with USCIS. But beware of issues of
potential "entry fraud", or so-called "intent issues".
While your filing of an I-130 petition is the first step, after marriage, where and how to process your
then-husband's second part of the appliication will depend on whether he will be in the U.S.
to file for an "Adjustment of Status", or whether to "Consular Process" his immigrant visa application
If your fiance is currently not in possession of any valid U.S. visa, and you are not yet legally married,
the best course of action would be to apply for his K-visa as your fiance, so he can enter the U.S. legally,
for the specific purpose of getting married.