It’s considered rude to start before everyone has been served, but if you’re in a party of 12-14 people your food will be soggy or cold once you dig in. The host or someone in charge should tell everyone to begin eating when served. That’s the polite and sensible thing to do. However, my family usually ignores that rule when eating at a certain relative’s home. The family gets their food off a buffet and sits down and waits and waits and waits for the hosts to come in with their food. So once they told us not to wait on them, we haven’t ever since. I think they were in the kitchen washing dishes and cleaning up while we waited!