Services and Advocacy for G.L.B.T. Elders, or SAGE, is opening its first senior center for lesbian, gay, bisexual and transgender people in the Bronx on Wednesday as part of a $1.5 million, city-funded expansion of L.G.B.T.-focused senior programs and support services across the five boroughs. The Bronx center will operate five days a week from rented space on the second floor of the Union Community Health Center on East 188th Street. It will offer a range of social, cultural, art and health programs, as well as hot lunches.