it sfunny how out of town ppl uaually say good shabbos to anyone as long as their jewish and in ny/lkwd chos vshalom! only to your gender
i think you should judge the situation- if you see a old women and you a boy i personally dont think theres anything wrong with smiling at her and wishing her good shabbos!
but if your a teenage boy and you see a teenage girl no you shouldnt say good shabbos to her if your trying to flirt (this also applys vica-versa)
if your just being polite/freindly then say good shabbos