April of 1988 was the first catalog featuring Athena. These parts were released for the 1989 year. That is the earliest, unless someone replaced the original group on the bike, or bought an old stock frame and hung new parts on it. Stylistically there's nothing wrong with this bike being built in 1989, though...so...Occam's razor sez not earlier than 1989. The same style and parts lag over into the early '90's.

By '92 almost everything was different (http://bulgier.net/pics/bike/Catalogs/basso92/). And earlier? More chrome...see the earlier catalogs on Bulgier's site.

So..'89, '90, '91. Pick which you like the best.