From Disney Food Blog
"UPDATE: We stopped by Space 220 and asked a Cast Member about this change. They told us that,
starting tomorrow (December 2nd) and going forward, the Space 220 Lounge will require reservations. There will still be a standby line for the bar, but minors will not be permitted. So if there are people under 21 in your group, you’ll need reservations for Space 220 no matter where you eat (the Lounge or the Dining Room). But if you can’t get reservations for the day you’ll be there, you can still walk up to sit at the bar without reserving your spot ahead of time."
Link to answer on PlanDisney
Space 220 bar