Like society season, “The Gilded Age” — the long-gestating, sweeping and, of course, soapy period series by “Downton Abbey” creator Julian Fellowes — is now in full-swing. But in this round, the examination of socio-economic and class hierarchy focuses on a distinctly American clash of old and new money in New York City’s post-industrial boom. Or, more specifically, the tony corner of Fifth Avenue and 61st Street (via the actual set in Troy, New York), where Robber Baron Dynasties are muscling their way into the Old Guard Establishment in 1882, as younger generations begin challenging stuffy, traditional mindsets, because maybe leisure class women actually want to have a career. (Cue a perplexed Dowager Countess, across the pond, asking, “What is a ‘weekend‘?”)