Bay seniors who have not filled their dance card for this weekend might want to join the nostalgia obsessed hoofers at the SF Swing Fest. Don’t worry if you can’t dance the Lindy, Charleston, Shag or Balboa. The weekend includes classes followed by live music, costume balls and contests at the 1916 Hotel Whitcomb near the Civic Center. You don’t even need to bring a partner. Tickets start at $50. Gosh, it sounds swell.