The main thing holding it up currently are environmental concerns around the launch site. Red tape essentially. The rocket has already done low altitude flights and static fires. It appears to work. It's quite a bit further along than SLS was a year before it's first mission. I'm well familiar with the concept of 'Elon time' but Starship flying next year is well within the realm of plausible, as long as they can iron out the launch site issues.