Neither 80's nor oldschool have a wiki entry so added both because of the specific style. I think we could only use one (preferably oldschool methinks) of those for pictures that are only drawn like 80's anime but originally come from modern artist.

The art style is 70's.

I think that 80s/70s etc. could probably implicate oldschool. If you're unsure, just put olschool, not a specific decade.

The manga is from the 70s. The anime series started in 1979 and finished in 1980. Movies based on the series were made in the 80s. It is both 70s and 80s...