ETIQUETTE: When to start eating
At a small table of two, four or even six people, when the delay will not be sufficient to cause the food to become cold or the souffle' to fall, it is certainly polite to wait to start eating until all have been served. In this case the hostess should pick up her implement first, and the others follow suit.
If the group is larger, however, it is not necessary to wait until all have been served. The hostess, if she is at all aware of her guests' comfort, will say, as soon as the first two or three guests have their food, "Please start--your dinner will get cold if you wait," and the guests take her at her word and start immediately. If the hostess says nothing, and you realize that her attention has been devoted to serving or supervising, or that she has simply forgotten to say anything, it is not incorrect to pick up your spoon or fork after three or four people have been served. The others will soon follow your lead. At family meals, as Mother or Father fills and passes the plates, the children should say, "May I please begin?" if they are not old enough to be expected to wait until one or two adults have started.