Ah. thumbs upNope. (And he actually said "twenty-something years before Gotham", which isn't necessarily definite.)
Plus there were no modern Mustangs in the 80s or 90s, and on a lesser note, the flip phones used in the show weren't like anything before 2002. I think Bruno Heller was just making a wild guess. I also don't think he was all that involved in the show's creative process after Season 3 from what I can tell.
Regardless, the V8 Mustang in Season 4 kills any chance of Gotham being set in the 20th Century.