What is proper etiquette when at a restaurant you order an entree that comes with a starter (like soup or a salad) that is brought out before the meal, and the person you are dining with did not?
You might suggest to your guest that they may want to order an appetizer to be served at the same time as your starter. If they decline, then they are implying their awareness of your starter and are essentially consenting to the disparity of the number of courses for your respective meals.
Alternately, you could ask your server to not delay in the serving of the entrees - i.e. don't wait for you to be done with your starter before "firing the entrees." ("Firing" entrees means finishing cooking them, plating them, and sending them to the table).
In modern small-plate restaurants, you would say "send the dishes as ready" - which means that the kitchen should just fire all the food, and send out whatever is ready first. Don't worry about coursing, just send it to the table, we'll figure it out.
As an aside, the likely reason that your entree comes with a starter is because it takes a little while to cook, and the starter buys time between the time that you place the order and the time the food hits the table. So you're still going to have a wait for the entrees a little. It's unavoidable. I'd suggest you take your time with the starter, and make good conversation.
Inside information: Kitchens - at least fine dining kitchens - hate the "order fire." That's when a table orders only entrees, no starters. The reason they hate it is because now it's a race to get the food on the table as quickly as possible. Certain dishes - for example duck, pot pies, and certain beef dishes, like Beef Wellington - require longer to cook. It's simple chemistry, it's not really negotiable. So if the guest gets a salad or a soup to munch on after a few minutes, and the starter takes 10 minutes to eat, then the guests are less likely to notice that it takes a total of 20 minutes or more for their entrees to hit the table. But if they dont order appetizers/starters, and they're sitting there at the table twiddling their thumbs, or especially if they suck at conversation, then they'll be disappointed that their food "took an hour." True story.